[a11y] Update semantics in bottom_navigation_bar.dart (flutter#150576)

issue: flutter#117997

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Author: hannah-hyj

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

@@ -605,6 +605,7 @@ class _BottomNavigationTile extends StatelessWidget {
 
     result = Semantics(
       selected: selected,
+      button: true,
       container: true,
       child: Stack(
         children: <Widget>[

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -2108,6 +2108,7 @@ void main() {
       matchesSemantics(
         label: 'AC\nTab 1 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         isSelected: true,
         hasTapAction: true,
@@ -2119,6 +2120,7 @@ void main() {
       matchesSemantics(
         label: 'Alarm\nTab 2 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2129,6 +2131,7 @@ void main() {
       matchesSemantics(
         label: 'Hot Tub\nTab 3 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2165,6 +2168,7 @@ void main() {
       matchesSemantics(
         label: 'AC\nTab 1 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         isSelected: true,
         hasTapAction: true,
@@ -2176,6 +2180,7 @@ void main() {
       matchesSemantics(
         label: 'Alarm\nTab 2 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2186,6 +2191,7 @@ void main() {
       matchesSemantics(
         label: 'Hot Tub\nTab 3 of 3',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2518,6 +2524,7 @@ void main() {
       matchesSemantics(
         label: 'Red\nTab 1 of 2',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         isSelected: true,
         hasTapAction: true,
@@ -2529,6 +2536,7 @@ void main() {
       matchesSemantics(
         label: 'Green\nTab 2 of 2',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2563,6 +2571,7 @@ void main() {
       matchesSemantics(
         label: 'Red\nTab 1 of 2',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         isSelected: true,
         hasTapAction: true,
@@ -2574,6 +2583,7 @@ void main() {
       matchesSemantics(
         label: 'Green\nTab 2 of 2',
         textDirection: TextDirection.ltr,
+        isButton: true,
         isFocusable: true,
         hasTapAction: true,
         hasFocusAction: true,
@@ -2754,6 +2764,7 @@ void main() {
                           children: <TestSemantics>[
                             TestSemantics(
                               flags: <SemanticsFlag>[
+                                SemanticsFlag.isButton,
                                 SemanticsFlag.isSelected,
                                 SemanticsFlag.isFocusable,
                               ],
@@ -2762,7 +2773,10 @@ void main() {
                               textDirection: TextDirection.ltr,
                             ),
                             TestSemantics(
-                              flags: <SemanticsFlag>[SemanticsFlag.isFocusable],
+                              flags: <SemanticsFlag>[
+                                SemanticsFlag.isButton,
+                                SemanticsFlag.isFocusable,
+                              ],
                               actions: <SemanticsAction>[SemanticsAction.tap, SemanticsAction.focus],
                               label: 'B\nTab 2 of 2',
                               textDirection: TextDirection.ltr,