Add button flag to NavigationDestination (#161568)

This PR is to add `Semantics.button` to `NavigationDestination` so that
when the switch control on iOS is turned on, it can traverse the
unselected destinations.

Fixes https://github.com/flutter/flutter/issues/161563



https://github.com/user-attachments/assets/b761aea6-d1d3-468b-b0a5-249fb03e08e3



## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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

@@ -996,6 +996,7 @@ class _NavigationBarDestinationSemantics extends StatelessWidget {
         return Semantics(
           selected: destinationInfo.selectedAnimation.isForwardOrCompleted,
           container: true,
+          button: true,
           child: child,
         );
       },

packages/flutter/test/material/navigation_bar_test.dart

@@ -460,6 +460,7 @@ void main() {
           destinations: const <Widget>[
             NavigationDestination(icon: Icon(Icons.ac_unit), label: 'AC'),
             NavigationDestination(icon: Icon(Icons.access_alarm), label: 'Alarm'),
+            NavigationDestination(icon: Icon(Icons.abc), label: 'ABC'),
           ],
         ),
       );
@@ -470,10 +471,11 @@ void main() {
     expect(
       tester.getSemantics(find.text('AC')),
       matchesSemantics(
-        label: 'AC\nTab 1 of 2',
+        label: 'AC\nTab 1 of 3',
         textDirection: TextDirection.ltr,
         isFocusable: true,
         isSelected: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -481,9 +483,21 @@ void main() {
     expect(
       tester.getSemantics(find.text('Alarm')),
       matchesSemantics(
-        label: 'Alarm\nTab 2 of 2',
+        label: 'Alarm\nTab 2 of 3',
         textDirection: TextDirection.ltr,
         isFocusable: true,
+        isButton: true,
+        hasTapAction: true,
+        hasFocusAction: true,
+      ),
+    );
+    expect(
+      tester.getSemantics(find.text('ABC')),
+      matchesSemantics(
+        label: 'ABC\nTab 3 of 3',
+        textDirection: TextDirection.ltr,
+        isFocusable: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -494,9 +508,10 @@ void main() {
     expect(
       tester.getSemantics(find.text('AC')),
       matchesSemantics(
-        label: 'AC\nTab 1 of 2',
+        label: 'AC\nTab 1 of 3',
         textDirection: TextDirection.ltr,
         isFocusable: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -504,10 +519,22 @@ void main() {
     expect(
       tester.getSemantics(find.text('Alarm')),
       matchesSemantics(
-        label: 'Alarm\nTab 2 of 2',
+        label: 'Alarm\nTab 2 of 3',
         textDirection: TextDirection.ltr,
         isFocusable: true,
         isSelected: true,
+        isButton: true,
+        hasTapAction: true,
+        hasFocusAction: true,
+      ),
+    );
+    expect(
+      tester.getSemantics(find.text('ABC')),
+      matchesSemantics(
+        label: 'ABC\nTab 3 of 3',
+        textDirection: TextDirection.ltr,
+        isFocusable: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -537,6 +564,7 @@ void main() {
         textDirection: TextDirection.ltr,
         isFocusable: true,
         isSelected: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -547,6 +575,7 @@ void main() {
         label: 'Alarm\nTab 2 of 2',
         textDirection: TextDirection.ltr,
         isFocusable: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -560,6 +589,7 @@ void main() {
         label: 'AC\nTab 1 of 2',
         textDirection: TextDirection.ltr,
         isFocusable: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),
@@ -571,6 +601,7 @@ void main() {
         textDirection: TextDirection.ltr,
         isFocusable: true,
         isSelected: true,
+        isButton: true,
         hasTapAction: true,
         hasFocusAction: true,
       ),