Next Gen UI demo (#1778)

First pass at a Next Generation UI demo app. The UI needs work, feedback
gratefully accepted.

## 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.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

next_gen_ui_demo/lib/common/ui_scaler.dart

@@ -0,0 +1,31 @@
+// Copyright 2023 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 'dart:math';
+
+import 'package:flutter/material.dart';
+
+class UiScaler extends StatelessWidget {
+  const UiScaler({
+    super.key,
+    required this.child,
+    required this.alignment,
+    this.referenceHeight = 1080,
+  });
+
+  final int referenceHeight;
+  final Widget child;
+  final Alignment alignment;
+
+  @override
+  Widget build(BuildContext context) {
+    final screenSize = MediaQuery.of(context).size;
+    final double scale = min(screenSize.height / referenceHeight, 1.0);
+    return Transform.scale(
+      scale: scale,
+      alignment: alignment,
+      child: child,
+    );
+  }
+}