[Fix]: Searchbar doesn't lose focus when tapped outside (#145232)

Added a Fix to search bar that allows it be unfocused when tapped anywhere outside the search bar.

I have attached below the app flow after implementing the fix.

https://github.com/flutter/flutter/assets/54017876/70915c47-9b77-4a43-a128-8706107f921f

Issue that gets resolved by this fix: #145096

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

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

@@ -1118,6 +1118,7 @@ class SearchBar extends StatefulWidget {
     this.leading,
     this.trailing,
     this.onTap,
+    this.onTapOutside,
     this.onChanged,
     this.onSubmitted,
     this.constraints,
@@ -1170,6 +1171,9 @@ class SearchBar extends StatefulWidget {
   /// Called when the user taps this search bar.
   final GestureTapCallback? onTap;
 
+  /// Called when the user taps outside the search bar.
+  final TapRegionCallback? onTapOutside;
+
   /// Invoked upon user input.
   final ValueChanged<String>? onChanged;
 
@@ -1397,6 +1401,7 @@ class _SearchBarState extends State<SearchBar> {
                           autofocus: widget.autoFocus,
                           onTap: widget.onTap,
                           onTapAlwaysCalled: true,
+                          onTapOutside: widget.onTapOutside,
                           focusNode: _focusNode,
                           onChanged: widget.onChanged,
                           onSubmitted: widget.onSubmitted,

packages/flutter/test/material/search_anchor_test.dart

@@ -3061,6 +3061,48 @@ void main() {
     expect(box.size.height, 32);
   });
 
+  testWidgets('Tapping outside searchbar should unfocus the searchbar on mobile', (WidgetTester tester) async {
+      final FocusNode focusNode = FocusNode(debugLabel: 'Test Node');
+      addTearDown(focusNode.dispose);
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: SearchAnchor(
+              builder: (BuildContext context, SearchController controller){
+                return SearchBar(
+                  controller: controller,
+                  onTap: () {
+                    controller.openView();
+                  },
+                  onTapOutside: (PointerDownEvent event) {
+                    focusNode.unfocus();
+                  },
+                  onChanged: (_) {
+                    controller.openView();
+                  },
+                  autoFocus: true,
+                  focusNode: focusNode,
+                );
+              },
+              suggestionsBuilder: (BuildContext context, SearchController controller){
+                return List<ListTile>.generate(5, (int index) {
+                  final String item = 'item $index';
+                  return ListTile(title: Text(item));
+                });
+              },
+            )
+          ),
+        ),
+      );
+      await tester.pump();
+      expect(focusNode.hasPrimaryFocus, isTrue);
+
+      await tester.tapAt(const Offset(50, 50));
+      await tester.pump();
+
+      expect(focusNode.hasPrimaryFocus, isFalse);
+    }, variant: TargetPlatformVariant.mobile());
+
   testWidgets('The default clear button only shows when text input is not empty '
       'on the search view', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(