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/pubspec.yaml

@@ -0,0 +1,21 @@
+name: cupertino_gallery
+description: A Flutter project showcasing supported Cupertino components.
+publish_to: "none"
+version: 1.0.0+1
+
+environment:
+  sdk: ^3.9.0-0
+
+dependencies:
+  flutter:
+    sdk: flutter
+  cupertino_icons: ^1.0.8
+
+dev_dependencies:
+  analysis_defaults:
+    path: ../analysis_defaults
+  flutter_test:
+    sdk: flutter
+
+flutter:
+  uses-material-design: true