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_page.dart

@@ -0,0 +1,75 @@
+import 'package:flutter/cupertino.dart';
+import 'widget_detail_page.dart';
+
+class WidgetsPage extends StatelessWidget {
+  const WidgetsPage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoPageScaffold(
+      child: CustomScrollView(
+        slivers: <Widget>[
+          CupertinoSliverNavigationBar(largeTitle: Text('Cupertino Gallery')),
+          SliverFillRemaining(
+            child: ListView(
+              children: [
+                CustomCupertinoListTile(title: 'Action Sheet'),
+                CustomCupertinoListTile(title: 'Activity Indicator'),
+                CustomCupertinoListTile(title: 'Alert Dialog'),
+                CustomCupertinoListTile(title: 'Button'),
+                CustomCupertinoListTile(title: 'Checkbox'),
+                CustomCupertinoListTile(title: 'Context Menu'),
+                CustomCupertinoListTile(title: 'Date Picker'),
+                CustomCupertinoListTile(title: 'List Tile'),
+                CustomCupertinoListTile(title: 'Picker'),
+                CustomCupertinoListTile(title: 'Popup Surface'),
+                CustomCupertinoListTile(title: 'Radio'),
+                CustomCupertinoListTile(title: 'Scrollbar'),
+                CustomCupertinoListTile(title: 'Search Text Field'),
+                CustomCupertinoListTile(title: 'Segmented Control'),
+                CustomCupertinoListTile(title: 'Sheet'),
+                CustomCupertinoListTile(title: 'Slider'),
+                CustomCupertinoListTile(title: 'Sliding Segmented Control'),
+                CustomCupertinoListTile(title: 'Switch'),
+                CustomCupertinoListTile(title: 'Text Field'),
+                CustomCupertinoListTile(title: 'Text Theme'),
+                CustomCupertinoListTile(title: 'Time Picker'),
+              ],
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+class CustomCupertinoListTile extends StatelessWidget {
+  const CustomCupertinoListTile({super.key, required this.title});
+
+  final String title;
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      onTap: () {
+        Navigator.of(context).push(
+          CupertinoPageRoute<void>(
+            builder: (BuildContext context) {
+              return WidgetDetailPage(title: title);
+            },
+          ),
+        );
+      },
+      child: Container(
+        padding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 12.0),
+        decoration: const BoxDecoration(
+          border: Border(bottom: BorderSide(color: CupertinoColors.separator)),
+        ),
+        child: Row(
+          mainAxisAlignment: MainAxisAlignment.spaceBetween,
+          children: <Widget>[Text(title), const Icon(CupertinoIcons.forward)],
+        ),
+      ),
+    );
+  }
+}