Add `CupertinoButton` interactive example (#93625)

examples/api/lib/cupertino/button/cupertino_button.0.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flutter code sample for CupertinoButton
+
+import 'package:flutter/cupertino.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
+  static const String _title = 'Flutter Code Sample';
+
+  @override
+  Widget build(BuildContext context) {
+    return const CupertinoApp(
+      title: _title,
+      home: MyStatelessWidget(),
+    );
+  }
+}
+
+class MyStatelessWidget extends StatelessWidget {
+  const MyStatelessWidget({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return Center(
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        children: <Widget>[
+          const CupertinoButton(
+            onPressed: null,
+            child: Text('Disabled'),
+          ),
+          const SizedBox(height: 30),
+          const CupertinoButton.filled(
+            onPressed: null,
+            child: Text('Disabled'),
+          ),
+          const SizedBox(height: 30),
+          CupertinoButton(
+            onPressed: () {},
+            child: const Text('Enabled'),
+          ),
+          const SizedBox(height: 30),
+          CupertinoButton.filled(
+            onPressed: () {},
+            child: const Text('Enabled'),
+          ),
+        ],
+      ),
+    );
+  }
+}

examples/api/test/cupertino/button/cupertino_button.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter_api_samples/cupertino/button/cupertino_button.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Has 4 CupertinoButton variants', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+
+    expect(find.byType(CupertinoButton), findsNWidgets(4));
+    expect(find.ancestor(of: find.text('Enabled'), matching: find.byType(CupertinoButton)), findsNWidgets(2));
+    expect(find.ancestor(of: find.text('Disabled'), matching: find.byType(CupertinoButton)), findsNWidgets(2));
+  });
+}

packages/flutter/lib/src/cupertino/button.dart

@@ -26,6 +26,13 @@ const EdgeInsets _kBackgroundButtonPadding = EdgeInsets.symmetric(
 /// [EdgeInsets.zero], should be used to prevent clipping larger [child]
 /// widgets.
 ///
+/// {@tool dartpad}
+/// This sample shows produces an enabled and disabled [CupertinoButton] and
+/// [CupertinoButton.filled].
+///
+/// ** See code in examples/api/lib/cupertino/button/cupertino_button.0.dart **
+/// {@end-tool}
+///
 /// See also:
 ///
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/buttons/>