Cupertino gallery app (#2715)

Resolves #2519 

Part of the larger effort to bring the samples/repo into a stable and
maintainable condition that _also_ remains useful. See: #2409

## 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 have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

cupertino_gallery/lib/widgets/action_sheet_page.dart

@@ -0,0 +1,49 @@
+import 'package:flutter/cupertino.dart';
+
+class ActionSheetPage extends StatelessWidget {
+  const ActionSheetPage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoPageScaffold(
+      navigationBar: const CupertinoNavigationBar(
+        middle: Text('Action Sheet'),
+      ),
+      child: Center(
+        child: CupertinoButton(
+          child: const Text('Show Action Sheet'),
+          onPressed: () {
+            showCupertinoModalPopup<void>(
+              context: context,
+              builder: (BuildContext context) => CupertinoActionSheet(
+                title: const Text('Title'),
+                message: const Text('Message'),
+                actions: <CupertinoActionSheetAction>[
+                  CupertinoActionSheetAction(
+                    child: const Text('Action One'),
+                    onPressed: () {
+                      Navigator.pop(context);
+                    },
+                  ),
+                  CupertinoActionSheetAction(
+                    child: const Text('Action Two'),
+                    onPressed: () {
+                      Navigator.pop(context);
+                    },
+                  )
+                ],
+                cancelButton: CupertinoActionSheetAction(
+                  isDefaultAction: true,
+                  onPressed: () {
+                    Navigator.pop(context);
+                  },
+                  child: const Text('Cancel'),
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+  }
+}