Add game_template (#1180)

Adds a template / sample for games built in Flutter, with all the bells and whistles, like ads, in-app purchases, audio, main menu, settings, and so on.

Co-authored-by: Parker Lougheed
Co-authored-by: Shams Zakhour

game_template/test/smoke_test.dart

@@ -0,0 +1,48 @@
+// Copyright 2022, the Flutter project authors. Please see the AUTHORS file
+// for details. 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_test/flutter_test.dart';
+import 'package:game_template/main.dart';
+import 'package:game_template/src/player_progress/persistence/memory_player_progress_persistence.dart';
+import 'package:game_template/src/settings/persistence/memory_settings_persistence.dart';
+
+void main() {
+  testWidgets('smoke test', (tester) async {
+    // Build our game and trigger a frame.
+    await tester.pumpWidget(MyApp(
+      settingsPersistence: MemoryOnlySettingsPersistence(),
+      playerProgressPersistence: MemoryOnlyPlayerProgressPersistence(),
+      adsController: null,
+      gamesServicesController: null,
+      inAppPurchaseController: null,
+    ));
+
+    // Verify that the 'Play' button is shown.
+    expect(find.text('Play'), findsOneWidget);
+
+    // Verify that the 'Settings' button is shown.
+    expect(find.text('Settings'), findsOneWidget);
+
+    // Go to 'Settings'.
+    await tester.tap(find.text('Settings'));
+    await tester.pumpAndSettle();
+    expect(find.text('Music'), findsOneWidget);
+
+    // Go back to main menu.
+    await tester.tap(find.text('Back'));
+    await tester.pumpAndSettle();
+
+    // Tap 'Play'.
+    await tester.tap(find.text('Play'));
+    await tester.pumpAndSettle();
+    expect(find.text('Select level'), findsOneWidget);
+
+    // Tap level 1.
+    await tester.tap(find.text('Level #1'));
+    await tester.pumpAndSettle();
+
+    // Find the first level's "tutorial" text.
+    expect(find.text('Drag the slider to 5% or above!'), findsOneWidget);
+  });
+}