Move context menus out of experimental (#2134)

Now that the context menu code is on stable, move the sample out of
experimental.

Fixes https://github.com/flutter/samples/issues/2110

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

---------

Co-authored-by: Brett Morgan <brett.morgan@gmail.com>

context_menus/lib/main.dart

@@ -0,0 +1,215 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+import 'anywhere_page.dart';
+import 'cascading_menu_page.dart';
+import 'custom_buttons_page.dart';
+import 'custom_menu_page.dart';
+import 'default_values_page.dart';
+import 'email_button_page.dart';
+import 'field_types_page.dart';
+import 'full_page.dart';
+import 'global_selection_page.dart';
+import 'image_page.dart';
+import 'modified_action_page.dart';
+import 'platform_selector.dart';
+import 'reordered_buttons_page.dart';
+
+void main() {
+  runApp(const MyApp());
+}
+
+class MyApp extends StatefulWidget {
+  const MyApp({
+    super.key,
+  });
+
+  @override
+  State<MyApp> createState() => _MyAppState();
+}
+
+class _MyAppState extends State<MyApp> {
+  void onChangedPlatform(TargetPlatform platform) {
+    setState(() {
+      debugDefaultTargetPlatformOverride = platform;
+    });
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    // On web, disable the browser's context menu everywhere so that the custom
+    // Flutter-rendered context menu shows.
+    if (kIsWeb) {
+      BrowserContextMenu.disableContextMenu();
+    }
+  }
+
+  @override
+  void dispose() {
+    if (kIsWeb) {
+      BrowserContextMenu.enableContextMenu();
+    }
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      debugShowCheckedModeBanner: false,
+      title: 'Flutter Context Menu Examples',
+      theme: ThemeData(
+        primarySwatch: Colors.blue,
+        platform: defaultTargetPlatform,
+        useMaterial3: true,
+      ),
+      initialRoute: '/',
+      routes: <String, Widget Function(BuildContext)>{
+        '/': (context) => MyHomePage(onChangedPlatform: onChangedPlatform),
+        AnywherePage.route: (context) =>
+            AnywherePage(onChangedPlatform: onChangedPlatform),
+        CustomButtonsPage.route: (context) =>
+            CustomButtonsPage(onChangedPlatform: onChangedPlatform),
+        CustomMenuPage.route: (context) =>
+            CustomMenuPage(onChangedPlatform: onChangedPlatform),
+        ReorderedButtonsPage.route: (context) =>
+            ReorderedButtonsPage(onChangedPlatform: onChangedPlatform),
+        EmailButtonPage.route: (context) =>
+            EmailButtonPage(onChangedPlatform: onChangedPlatform),
+        ImagePage.route: (context) =>
+            ImagePage(onChangedPlatform: onChangedPlatform),
+        FieldTypesPage.route: (context) =>
+            FieldTypesPage(onChangedPlatform: onChangedPlatform),
+        FullPage.route: (context) =>
+            FullPage(onChangedPlatform: onChangedPlatform),
+        ModifiedActionPage.route: (context) =>
+            ModifiedActionPage(onChangedPlatform: onChangedPlatform),
+        GlobalSelectionPage.route: (context) =>
+            GlobalSelectionPage(onChangedPlatform: onChangedPlatform),
+        DefaultValuesPage.route: (context) =>
+            DefaultValuesPage(onChangedPlatform: onChangedPlatform),
+        CascadingMenuPage.route: (context) =>
+            CascadingMenuPage(onChangedPlatform: onChangedPlatform),
+      },
+    );
+  }
+}
+
+class MyHomePage extends StatelessWidget {
+  const MyHomePage({
+    super.key,
+    required this.onChangedPlatform,
+  });
+
+  final PlatformCallback onChangedPlatform;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Context Menu Demos'),
+        actions: <Widget>[
+          PlatformSelector(
+            onChangedPlatform: onChangedPlatform,
+          ),
+        ],
+      ),
+      body: ListView(
+        children: const <Widget>[
+          _MyListItem(
+            route: AnywherePage.route,
+            title: AnywherePage.title,
+            subtitle: AnywherePage.subtitle,
+          ),
+          _MyListItem(
+            route: GlobalSelectionPage.route,
+            title: GlobalSelectionPage.title,
+            subtitle: GlobalSelectionPage.subtitle,
+          ),
+          _MyListItem(
+            route: ImagePage.route,
+            title: ImagePage.title,
+            subtitle: ImagePage.subtitle,
+          ),
+          _MyListItem(
+            route: CustomButtonsPage.route,
+            title: CustomButtonsPage.title,
+            subtitle: CustomButtonsPage.subtitle,
+          ),
+          _MyListItem(
+            route: CustomMenuPage.route,
+            title: CustomMenuPage.title,
+            subtitle: CustomMenuPage.subtitle,
+          ),
+          _MyListItem(
+            route: EmailButtonPage.route,
+            title: EmailButtonPage.title,
+            subtitle: EmailButtonPage.subtitle,
+          ),
+          _MyListItem(
+            route: ReorderedButtonsPage.route,
+            title: ReorderedButtonsPage.title,
+            subtitle: ReorderedButtonsPage.subtitle,
+          ),
+          _MyListItem(
+            route: ModifiedActionPage.route,
+            title: ModifiedActionPage.title,
+            subtitle: ModifiedActionPage.subtitle,
+          ),
+          _MyListItem(
+            route: FieldTypesPage.route,
+            title: FieldTypesPage.title,
+            subtitle: FieldTypesPage.subtitle,
+          ),
+          _MyListItem(
+            route: DefaultValuesPage.route,
+            title: DefaultValuesPage.title,
+            subtitle: DefaultValuesPage.subtitle,
+          ),
+          _MyListItem(
+            route: CascadingMenuPage.route,
+            title: CascadingMenuPage.title,
+            subtitle: CascadingMenuPage.subtitle,
+          ),
+          _MyListItem(
+            route: FullPage.route,
+            title: FullPage.title,
+            subtitle: FullPage.subtitle,
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+class _MyListItem extends StatelessWidget {
+  const _MyListItem({
+    required this.route,
+    required this.subtitle,
+    required this.title,
+  });
+
+  final String route;
+  final String subtitle;
+  final String title;
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      onTap: () {
+        Navigator.of(context).pushNamed(route);
+      },
+      child: Card(
+        margin: const EdgeInsets.all(12.0),
+        child: Padding(
+          padding: const EdgeInsets.all(24.0),
+          child: ListTile(
+            title: Text(title),
+            subtitle: Text(subtitle),
+          ),
+        ),
+      ),
+    );
+  }
+}