Migrate testing_app to UIScene lifecycle (#2836)

## Summary
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- Migrate `testing_app` iOS project to the UIScene lifecycle as per the
[migration
guide](https://docs.flutter.dev/release/breaking-changes/uiscenedelegate)
- Update `AppDelegate.swift` to use `@main`,
`FlutterImplicitEngineDelegate`, and move plugin registration to
`didInitializeImplicitFlutterEngine`
- Add `UIApplicationSceneManifest` to `Info.plist`

Part of flutter/flutter#176957

## Test plan
- [x] Ran `testing_app` on iOS simulator — app launches and works
correctly

---------

Co-authored-by: Eric Windmill <eric@ericwindmill.com>

compass_app/app/lib/routing/router.dart

@@ -14,7 +14,8 @@ import '../ui/auth/login/widgets/login_screen.dart';
 import '../ui/auth/logout/view_models/logout_viewmodel.dart';
 import '../ui/booking/view_models/booking_viewmodel.dart';
 import '../ui/booking/widgets/booking_screen.dart';
-import '../ui/home/widgets/home_screen_container.dart';
+import '../ui/home/view_models/home_viewmodel.dart';
+import '../ui/home/widgets/home_screen.dart';
 import '../ui/results/view_models/results_viewmodel.dart';
 import '../ui/results/widgets/results_screen.dart';
 import '../ui/search_form/view_models/search_form_viewmodel.dart';