[a11y] Fix date picker cannot focus on the edit field (#143117)

fixes: [DatePicker edit field](https://github.com/flutter/flutter/issues/143116) 

https://b.corp.google.com/issues/322173632

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

@@ -394,6 +394,7 @@ class _DatePickerModeToggleButtonState extends State<_DatePickerModeToggleButton
               label: MaterialLocalizations.of(context).selectYearSemanticsLabel,
               excludeSemantics: true,
               button: true,
+              container: true,
               child: SizedBox(
                 height: _subHeaderHeight,
                 child: InkWell(

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

@@ -867,7 +867,9 @@ class _DatePickerHeader extends StatelessWidget {
 
     switch (orientation) {
       case Orientation.portrait:
-        return SizedBox(
+        return Semantics(
+          container: true,
+          child: SizedBox(
             height: _datePickerHeaderPortraitHeight,
             child: Material(
               color: backgroundColor,
@@ -887,16 +889,22 @@ class _DatePickerHeader extends StatelessWidget {
                       children: <Widget>[
                         Expanded(child: title),
                         if (entryModeButton != null)
-                        entryModeButton!,
+                         Semantics(
+                          container: true,
+                          child: entryModeButton,
+                        ),
                       ],
                     ),
                   ],
                 ),
               ),
             ),
+          ),
         );
       case Orientation.landscape:
-        return SizedBox(
+        return Semantics(
+          container: true,
+          child:SizedBox(
             width: _datePickerHeaderLandscapeWidth,
             child: Material(
               color: backgroundColor,
@@ -922,11 +930,15 @@ class _DatePickerHeader extends StatelessWidget {
                   if (entryModeButton != null)
                     Padding(
                       padding: const EdgeInsets.symmetric(horizontal: 4),
+                      child: Semantics(
+                        container: true,
                         child: entryModeButton,
                       ),
+                    ),
                 ],
               ),
             ),
+          ),
         );
     }
   }

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

@@ -256,11 +256,14 @@ class _InputDatePickerFormFieldState extends State<InputDatePickerFormField> {
       ?? theme.inputDecorationTheme.border
       ?? (useMaterial3 ? const OutlineInputBorder() : const UnderlineInputBorder());
 
-    return TextFormField(
+    return Semantics(
+      container: true,
+      child: TextFormField(
         decoration: InputDecoration(
           hintText: widget.fieldHintText ?? localizations.dateHelpText,
           labelText: widget.fieldLabelText ?? localizations.dateInputLabel,
-      ).applyDefaults(inputTheme
+        ).applyDefaults(
+          inputTheme
               .merge(datePickerTheme.inputDecorationTheme)
               .copyWith(border: effectiveInputBorder),
         ),
@@ -271,6 +274,7 @@ class _InputDatePickerFormFieldState extends State<InputDatePickerFormField> {
         autofocus: widget.autofocus,
         controller: _controller,
         focusNode: widget.focusNode,
+      ),
     );
   }
 }

packages/flutter/test/material/date_picker_test.dart

@@ -13,6 +13,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import '../widgets/clipboard_utils.dart';
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
@@ -1577,6 +1578,13 @@ void main() {
     });
 
     testWidgets('input mode', (WidgetTester tester) async {
+      // Fill the clipboard so that the Paste option is available in the text
+      // selection menu.
+      final MockClipboard mockClipboard = MockClipboard();
+      tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(SystemChannels.platform, mockClipboard.handleMethodCall);
+      await Clipboard.setData(const ClipboardData(text: 'Clipboard data'));
+      addTearDown(() => tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(SystemChannels.platform, null));
+
       final SemanticsHandle semantics = tester.ensureSemantics();
 
       initialEntryMode = DatePickerEntryMode.input;
@@ -1596,7 +1604,20 @@ void main() {
           isFocusable: true,
         ));
 
-        // The semantics of the InputDatePickerFormField are tested in its tests.
+        expect(tester.getSemantics(find.byType(EditableText)), matchesSemantics(
+          label: 'Enter Date',
+          isTextField: true,
+          isFocused: true,
+          value: '01/15/2016',
+          hasTapAction: true,
+          hasSetTextAction: true,
+          hasSetSelectionAction: true,
+          hasCopyAction: true,
+          hasCutAction: true,
+          hasPasteAction: true,
+          hasMoveCursorBackwardByCharacterAction: true,
+          hasMoveCursorBackwardByWordAction: true,
+        ));
 
         // Ok/Cancel buttons
         expect(tester.getSemantics(find.text('OK')), matchesSemantics(