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/reordered_buttons_page.dart

@@ -0,0 +1,96 @@
+import 'dart:collection';
+
+import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+import 'constants.dart';
+import 'platform_selector.dart';
+
+class ReorderedButtonsPage extends StatelessWidget {
+  ReorderedButtonsPage({
+    super.key,
+    required this.onChangedPlatform,
+  });
+
+  static const String route = 'reordered-buttons';
+  static const String title = 'Reordered Buttons';
+  static const String subtitle = 'The usual buttons, but in a different order.';
+  static const String url = '$kCodeUrl/reordered_buttons_page.dart';
+
+  final PlatformCallback onChangedPlatform;
+
+  final TextEditingController _controllerNormal = TextEditingController(
+    text: 'This button has the default buttons for reference.',
+  );
+
+  final TextEditingController _controllerReordered = TextEditingController(
+    text: 'This field has reordered buttons.',
+  );
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text(ReorderedButtonsPage.title),
+        actions: <Widget>[
+          PlatformSelector(
+            onChangedPlatform: onChangedPlatform,
+          ),
+          IconButton(
+            icon: const Icon(Icons.code),
+            onPressed: () async {
+              if (!await launchUrl(Uri.parse(url))) {
+                throw 'Could not launch $url';
+              }
+            },
+          ),
+        ],
+      ),
+      body: Center(
+        child: SizedBox(
+          width: 300.0,
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              TextField(
+                maxLines: 2,
+                controller: _controllerNormal,
+              ),
+              const SizedBox(height: 20.0),
+              TextField(
+                controller: _controllerReordered,
+                maxLines: 2,
+                contextMenuBuilder: (context, editableTextState) {
+                  // Reorder the button datas by type.
+                  final HashMap<ContextMenuButtonType, ContextMenuButtonItem>
+                      buttonItemsMap =
+                      HashMap<ContextMenuButtonType, ContextMenuButtonItem>();
+                  for (ContextMenuButtonItem buttonItem
+                      in editableTextState.contextMenuButtonItems) {
+                    buttonItemsMap[buttonItem.type] = buttonItem;
+                  }
+                  final List<ContextMenuButtonItem> reorderedButtonItems =
+                      <ContextMenuButtonItem>[
+                    if (buttonItemsMap
+                        .containsKey(ContextMenuButtonType.selectAll))
+                      buttonItemsMap[ContextMenuButtonType.selectAll]!,
+                    if (buttonItemsMap.containsKey(ContextMenuButtonType.paste))
+                      buttonItemsMap[ContextMenuButtonType.paste]!,
+                    if (buttonItemsMap.containsKey(ContextMenuButtonType.copy))
+                      buttonItemsMap[ContextMenuButtonType.copy]!,
+                    if (buttonItemsMap.containsKey(ContextMenuButtonType.cut))
+                      buttonItemsMap[ContextMenuButtonType.cut]!,
+                  ];
+                  return AdaptiveTextSelectionToolbar.buttonItems(
+                    anchors: editableTextState.contextMenuAnchors,
+                    buttonItems: reorderedButtonItems,
+                  );
+                },
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}