Add scrollbar for menus (#140941)

Fixes #140162

This PR is to add a scrollbar for MenuAnchor and DropdownMenu for all platforms when height is limited. Previously, a scrollbar only shows on desktop platforms. This PR also disabled scrollbar's overscroll for MenuAnchor and DropdownMenu.

<img src="https://github.com/flutter/flutter/assets/36861262/9ca3d4d0-415f-43bf-9d2b-df96a42db620" width="250"/><img src="https://github.com/flutter/flutter/assets/36861262/18da8d02-586b-4aa4-b647-927691542429" width="350"/>

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

@@ -26,6 +26,7 @@ import 'menu_button_theme.dart';
 import 'menu_style.dart';
 import 'menu_theme.dart';
 import 'radio.dart';
+import 'scrollbar.dart';
 import 'text_button.dart';
 import 'text_theme.dart';
 import 'theme.dart';
@@ -3369,6 +3370,8 @@ class _MenuPanel extends StatefulWidget {
 }
 
 class _MenuPanelState extends State<_MenuPanel> {
+  ScrollController scrollController = ScrollController();
+
   @override
   Widget build(BuildContext context) {
     final MenuStyle? themeStyle;
@@ -3454,14 +3457,28 @@ class _MenuPanelState extends State<_MenuPanel> {
         clipBehavior: widget.clipBehavior,
         child: Padding(
           padding: resolvedPadding,
-          child: SingleChildScrollView(
-            scrollDirection: widget.orientation,
-            child: Flex(
-              crossAxisAlignment: CrossAxisAlignment.start,
-              textDirection: Directionality.of(context),
-              direction: widget.orientation,
-              mainAxisSize: MainAxisSize.min,
-              children: widget.children,
+          child: ScrollConfiguration(
+            behavior: ScrollConfiguration.of(context).copyWith(
+              scrollbars: false,
+              overscroll: false,
+              physics: const ClampingScrollPhysics(),
+            ),
+            child: PrimaryScrollController(
+              controller: scrollController,
+              child: Scrollbar(
+                thumbVisibility: true,
+                child: SingleChildScrollView(
+                  controller: scrollController,
+                  scrollDirection: widget.orientation,
+                  child: Flex(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    textDirection: Directionality.of(context),
+                    direction: widget.orientation,
+                    mainAxisSize: MainAxisSize.min,
+                    children: widget.children,
+                  ),
+                ),
+              ),
             ),
           ),
         ),

packages/flutter/test/material/dropdown_menu_test.dart

@@ -1907,6 +1907,31 @@ void main() {
     expect(selectionCount, 1);
     expect(tester.takeException(), isNull);
   });
+
+  testWidgets('Menu shows scrollbar when height is limited', (WidgetTester tester) async {
+    final List<DropdownMenuEntry<TestMenu>> menuItems = <DropdownMenuEntry<TestMenu>>[
+      DropdownMenuEntry<TestMenu>(
+        value: TestMenu.mainMenu0,
+        label: 'Item 0',
+        style: MenuItemButton.styleFrom(
+          minimumSize: const Size.fromHeight(1000),
+        )
+      ),
+    ];
+
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: DropdownMenu<TestMenu>(
+          dropdownMenuEntries: menuItems,
+        ),
+      ),
+    ));
+
+    await tester.tap(find.byType(DropdownMenu<TestMenu>));
+    await tester.pumpAndSettle();
+
+    expect(find.byType(Scrollbar), findsOneWidget);
+  }, variant: TargetPlatformVariant.all());
 }
 
 enum TestMenu {

packages/flutter/test/material/menu_anchor_test.dart

@@ -472,10 +472,9 @@ void main() {
     await tester.tap(find.text('Main Menu'));
     await tester.pumpAndSettle();
 
-    expect(find.byType(Scrollbar), findsOneWidget);
     // Test Scrollbar thumb color.
     expect(
-      find.byType(Scrollbar),
+      find.byType(Scrollbar).last,
       paints..rrect(color: const Color(0xffff0000)),
     );
 
@@ -521,10 +520,9 @@ void main() {
     await tester.tap(find.text('Main Menu'));
     await tester.pumpAndSettle();
 
-    expect(find.byType(Scrollbar), findsOneWidget);
     // Scrollbar thumb color should be updated.
     expect(
-      find.byType(Scrollbar),
+      find.byType(Scrollbar).last,
       paints..rrect(color: const Color(0xff00ff00)),
     );
   }, variant: TargetPlatformVariant.desktop());