Add `onSubmitted` property to `SearchBar` (#129365)

Fixes #126551

This PR is to add `onSubmitted` property to `SearchBar`.

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

@@ -996,6 +996,7 @@ class SearchBar extends StatefulWidget {
     this.trailing,
     this.onTap,
     this.onChanged,
+    this.onSubmitted,
     this.constraints,
     this.elevation,
     this.backgroundColor,
@@ -1044,6 +1045,10 @@ class SearchBar extends StatefulWidget {
   /// Invoked upon user input.
   final ValueChanged<String>? onChanged;
 
+  /// Called when the user indicates that they are done editing the text in the
+  /// field.
+  final ValueChanged<String>? onSubmitted;
+
   /// Optional size constraints for the search bar.
   ///
   /// If null, the value of [SearchBarThemeData.constraints] will be used. If
@@ -1236,6 +1241,7 @@ class _SearchBarState extends State<SearchBar> {
                       child: TextField(
                         focusNode: _focusNode,
                         onChanged: widget.onChanged,
+                        onSubmitted: widget.onSubmitted,
                         controller: widget.controller,
                         style: effectiveTextStyle,
                         decoration: InputDecoration(

packages/flutter/test/material/search_anchor_test.dart

@@ -270,6 +270,26 @@ void main() {
     expect(changeCount, 2);
   });
 
+  testWidgets('SearchBar respects onSubmitted property', (WidgetTester tester) async {
+    String submittedQuery = '';
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: SearchBar(
+            onSubmitted: (String text) {
+              submittedQuery = text;
+            },
+          ),
+        ),
+      ),
+    );
+
+    await tester.enterText(find.byType(SearchBar), 'query');
+    await tester.testTextInput.receiveAction(TextInputAction.done);
+
+    expect(submittedQuery, equals('query'));
+  });
+
   testWidgets('SearchBar respects constraints property', (WidgetTester tester) async {
     const BoxConstraints constraints = BoxConstraints(maxWidth: 350.0, minHeight: 80);
     await tester.pumpWidget(