Fix default avatar icon theme size for Material 2 (#152307)

fixes [ActionChip avatar still does not respect padding](https://github.com/flutter/flutter/issues/116508)

### Code sample

<details>
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(brightness: Brightness.dark, useMaterial3: false),
      home: Scaffold(
        body: Center(
          child: Builder(
            builder: (BuildContext context) {
              return Chip(
                padding: const EdgeInsets.all(16.0),
                avatar: const Icon(Icons.favorite),
                label: const Text('Chip A'),
                onDeleted: () {},
              );
            },
          ),
        ),
      ),
    );
  }
}
```

</details>

### Before

<img width="490" alt="Screenshot 2024-07-25 at 16 24 08" src="https://github.com/user-attachments/assets/45408aa2-b3ab-4ff9-ae72-53a91c87c76a">

### After

<img width="490" alt="Screenshot 2024-07-25 at 16 23 56" src="https://github.com/user-attachments/assets/07ba367d-9ca3-46cc-8122-d1155dd2f32b">

packages/flutter/lib/src/material/chip.dart

@@ -1369,7 +1369,7 @@ class _RawChipState extends State<RawChip> with MaterialStateMixin, TickerProvid
     final TextStyle resolvedLabelStyle = effectiveLabelStyle.copyWith(color: resolvedLabelColor);
     final Widget? avatar = iconTheme != null && hasAvatar
       ? IconTheme.merge(
-          data: theme.useMaterial3 ? chipDefaults.iconTheme!.merge(iconTheme) : iconTheme,
+          data: chipDefaults.iconTheme!.merge(iconTheme),
           child: widget.avatar!,
         )
       : widget.avatar;

packages/flutter/lib/src/material/chip_theme.dart

@@ -276,6 +276,7 @@ class ChipThemeData with Diagnosticable {
       brightness: brightness,
       elevation: 0.0,
       pressElevation: 8.0,
+      iconTheme: const IconThemeData(size: 18.0),
     );
   }
 

packages/flutter/test/material/chip_test.dart

@@ -231,83 +231,6 @@ Finder findTooltipContainer(String tooltipText) {
 }
 
 void main() {
-  testWidgets('M2 Chip defaults', (WidgetTester tester) async {
-    late TextTheme textTheme;
-
-    Widget buildFrame(Brightness brightness) {
-      return MaterialApp(
-        theme: ThemeData(brightness: brightness, useMaterial3: false),
-        home: Scaffold(
-          body: Center(
-            child: Builder(
-              builder: (BuildContext context) {
-                textTheme = Theme.of(context).textTheme;
-                return Chip(
-                  avatar: const CircleAvatar(child: Text('A')),
-                  label: const Text('Chip A'),
-                  onDeleted: () { },
-                );
-              },
-            ),
-          ),
-        ),
-      );
-    }
-
-    await tester.pumpWidget(buildFrame(Brightness.light));
-    expect(getMaterialBox(tester), paints..rrect()..circle(color: const Color(0xff1976d2)));
-    expect(tester.getSize(find.byType(Chip)), const Size(156.0, 48.0));
-    expect(getMaterial(tester).color, null);
-    expect(getMaterial(tester).elevation, 0);
-    expect(getMaterial(tester).shape, const StadiumBorder());
-    expect(getIconData(tester).color?.value, 0xffffffff);
-    expect(getIconData(tester).opacity, null);
-    expect(getIconData(tester).size, null);
-
-    TextStyle labelStyle = getLabelStyle(tester, 'Chip A').style;
-    expect(labelStyle.color?.value, 0xde000000);
-    expect(labelStyle.fontFamily, textTheme.bodyLarge?.fontFamily);
-    expect(labelStyle.fontFamilyFallback, textTheme.bodyLarge?.fontFamilyFallback);
-    expect(labelStyle.fontFeatures, textTheme.bodyLarge?.fontFeatures);
-    expect(labelStyle.fontSize, textTheme.bodyLarge?.fontSize);
-    expect(labelStyle.fontStyle, textTheme.bodyLarge?.fontStyle);
-    expect(labelStyle.fontWeight, textTheme.bodyLarge?.fontWeight);
-    expect(labelStyle.height, textTheme.bodyLarge?.height);
-    expect(labelStyle.inherit, textTheme.bodyLarge?.inherit);
-    expect(labelStyle.leadingDistribution, textTheme.bodyLarge?.leadingDistribution);
-    expect(labelStyle.letterSpacing, textTheme.bodyLarge?.letterSpacing);
-    expect(labelStyle.overflow, textTheme.bodyLarge?.overflow);
-    expect(labelStyle.textBaseline, textTheme.bodyLarge?.textBaseline);
-    expect(labelStyle.wordSpacing, textTheme.bodyLarge?.wordSpacing);
-
-    await tester.pumpWidget(buildFrame(Brightness.dark));
-    await tester.pumpAndSettle(); // Theme transition animation
-    expect(getMaterialBox(tester), paints..rrect(color: const Color(0x1fffffff)));
-    expect(tester.getSize(find.byType(Chip)), const Size(156.0, 48.0));
-    expect(getMaterial(tester).color, null);
-    expect(getMaterial(tester).elevation, 0);
-    expect(getMaterial(tester).shape, const StadiumBorder());
-    expect(getIconData(tester).color?.value, 0xffffffff);
-    expect(getIconData(tester).opacity, null);
-    expect(getIconData(tester).size, null);
-
-    labelStyle = getLabelStyle(tester, 'Chip A').style;
-    expect(labelStyle.color?.value, 0xdeffffff);
-    expect(labelStyle.fontFamily, textTheme.bodyLarge?.fontFamily);
-    expect(labelStyle.fontFamilyFallback, textTheme.bodyLarge?.fontFamilyFallback);
-    expect(labelStyle.fontFeatures, textTheme.bodyLarge?.fontFeatures);
-    expect(labelStyle.fontSize, textTheme.bodyLarge?.fontSize);
-    expect(labelStyle.fontStyle, textTheme.bodyLarge?.fontStyle);
-    expect(labelStyle.fontWeight, textTheme.bodyLarge?.fontWeight);
-    expect(labelStyle.height, textTheme.bodyLarge?.height);
-    expect(labelStyle.inherit, textTheme.bodyLarge?.inherit);
-    expect(labelStyle.leadingDistribution, textTheme.bodyLarge?.leadingDistribution);
-    expect(labelStyle.letterSpacing, textTheme.bodyLarge?.letterSpacing);
-    expect(labelStyle.overflow, textTheme.bodyLarge?.overflow);
-    expect(labelStyle.textBaseline, textTheme.bodyLarge?.textBaseline);
-    expect(labelStyle.wordSpacing, textTheme.bodyLarge?.wordSpacing);
-  });
-
   testWidgets('M3 Chip defaults', (WidgetTester tester) async {
     late TextTheme textTheme;
     final ThemeData lightTheme = ThemeData.light();
@@ -4484,7 +4407,7 @@ void main() {
     expect(box.size, equals(const Size(128, 32.0 + 16.0)));
     expect(textBox.size, equals(const Size(56, 14)));
     expect(iconBox.size, equals(const Size(18, 18)));
-    expect(avatarBox.size, equals(const Size(24, 24)));
+    expect(avatarBox.size, equals(const Size(18, 18)));
     expect(textBox.top, equals(17));
     expect(box.bottom - textBox.bottom, equals(17));
     expect(textBox.left, equals(372));
@@ -4499,7 +4422,7 @@ void main() {
     expect(box.size, equals(const Size(128, 60)));
     expect(textBox.size, equals(const Size(56, 14)));
     expect(iconBox.size, equals(const Size(18, 18)));
-    expect(avatarBox.size, equals(const Size(24, 24)));
+    expect(avatarBox.size, equals(const Size(18, 18)));
     expect(textBox.top, equals(23));
     expect(box.bottom - textBox.bottom, equals(23));
     expect(textBox.left, equals(372));
@@ -4514,7 +4437,7 @@ void main() {
     expect(box.size, equals(const Size(128, 36)));
     expect(textBox.size, equals(const Size(56, 14)));
     expect(iconBox.size, equals(const Size(18, 18)));
-    expect(avatarBox.size, equals(const Size(24, 24)));
+    expect(avatarBox.size, equals(const Size(18, 18)));
     expect(textBox.top, equals(11));
     expect(box.bottom - textBox.bottom, equals(11));
     expect(textBox.left, equals(372));
@@ -4531,7 +4454,7 @@ void main() {
     expect(box.size, equals(const Size(128, 36)));
     expect(textBox.size, equals(const Size(56, 14)));
     expect(iconBox.size, equals(const Size(18, 18)));
-    expect(avatarBox.size, equals(const Size(24, 24)));
+    expect(avatarBox.size, equals(const Size(18, 18)));
     expect(textBox.top, equals(11));
     expect(box.bottom - textBox.bottom, equals(11));
     expect(textBox.left, equals(372));
@@ -5489,9 +5412,9 @@ void main() {
       expect(getMaterial(tester).color, null);
       expect(getMaterial(tester).elevation, 0);
       expect(getMaterial(tester).shape, const StadiumBorder());
-      expect(getIconData(tester).color?.value, 0xffffffff);
+      expect(getIconData(tester).color, const Color(0xdd000000));
       expect(getIconData(tester).opacity, null);
-      expect(getIconData(tester).size, null);
+      expect(getIconData(tester).size, 18.0);
 
       TextStyle labelStyle = getLabelStyle(tester, 'Chip A').style;
       expect(labelStyle.color?.value, 0xde000000);
@@ -5518,7 +5441,7 @@ void main() {
       expect(getMaterial(tester).shape, const StadiumBorder());
       expect(getIconData(tester).color?.value, 0xffffffff);
       expect(getIconData(tester).opacity, null);
-      expect(getIconData(tester).size, null);
+      expect(getIconData(tester).size, 18.0);
 
       labelStyle = getLabelStyle(tester, 'Chip A').style;
       expect(labelStyle.color?.value, 0xdeffffff);

packages/flutter/test/material/chip_theme_test.dart

@@ -613,6 +613,7 @@ void main() {
       selectedShadowColor: Colors.black,
       showCheckmark: false,
       checkmarkColor: Colors.black,
+      iconTheme: const IconThemeData(size: 26.0),
     );
     final ChipThemeData chipThemeWhite = ChipThemeData.fromDefaults(
       secondaryColor: Colors.white,
@@ -630,6 +631,7 @@ void main() {
       selectedShadowColor: Colors.white,
       showCheckmark: true,
       checkmarkColor: Colors.white,
+      iconTheme: const IconThemeData(size: 22.0),
     );
 
     final ChipThemeData lerp = ChipThemeData.lerp(chipThemeBlack, chipThemeWhite, 0.5)!;
@@ -653,7 +655,7 @@ void main() {
     expect(lerp.elevation, 3.0);
     expect(lerp.pressElevation, 7.0);
     expect(lerp.checkmarkColor, equals(middleGrey));
-    expect(lerp.iconTheme, isNull);
+    expect(lerp.iconTheme, const IconThemeData(size: 24.0));
 
     expect(ChipThemeData.lerp(null, null, 0.25), isNull);
 
@@ -677,7 +679,7 @@ void main() {
     expect(lerpANull25.elevation, 1.25);
     expect(lerpANull25.pressElevation, 2.5);
     expect(lerpANull25.checkmarkColor, equals(Colors.white.withAlpha(0x40)));
-    expect(lerp.iconTheme, isNull);
+    expect(lerpANull25.iconTheme, const IconThemeData(size: 5.5));
 
     final ChipThemeData lerpANull75 = ChipThemeData.lerp(null, chipThemeWhite, 0.75)!;
     expect(lerpANull75.backgroundColor, equals(Colors.black.withAlpha(0x17)));
@@ -699,6 +701,7 @@ void main() {
     expect(lerpANull75.elevation, 3.75);
     expect(lerpANull75.pressElevation, 7.5);
     expect(lerpANull75.checkmarkColor, equals(Colors.white.withAlpha(0xbf)));
+    expect(lerpANull75.iconTheme, const IconThemeData(size: 16.5));
 
     final ChipThemeData lerpBNull25 = ChipThemeData.lerp(chipThemeBlack, null, 0.25)!;
     expect(lerpBNull25.backgroundColor, equals(Colors.white.withAlpha(0x17)));
@@ -720,7 +723,7 @@ void main() {
     expect(lerpBNull25.elevation, 0.75);
     expect(lerpBNull25.pressElevation, 3.0);
     expect(lerpBNull25.checkmarkColor, equals(Colors.black.withAlpha(0xbf)));
-    expect(lerp.iconTheme, isNull);
+    expect(lerpBNull25.iconTheme, const IconThemeData(size: 19.5));
 
     final ChipThemeData lerpBNull75 = ChipThemeData.lerp(chipThemeBlack, null, 0.75)!;
     expect(lerpBNull75.backgroundColor, equals(Colors.white.withAlpha(0x08)));
@@ -742,7 +745,7 @@ void main() {
     expect(lerpBNull75.elevation, 0.25);
     expect(lerpBNull75.pressElevation, 1.0);
     expect(lerpBNull75.checkmarkColor, equals(Colors.black.withAlpha(0x40)));
-    expect(lerp.iconTheme, isNull);
+    expect(lerpBNull75.iconTheme, const IconThemeData(size: 6.5));
   });
 
   testWidgets('Chip uses stateful color from chip theme', (WidgetTester tester) async {