[add-to-app] Wish for the add_to_app samples using SwiftUI to match the new updated docs

[sethladd]

Use case

We've updated https://docs.flutter.dev/add-to-app/ios/add-flutter-screen which is great!

Apparently, the add to app samples over in https://github.com/flutter/samples/tree/main/add_to_app have not yet been updated.

Proposal

We should update the SwiftUI based samples in https://github.com/flutter/samples/tree/main/add_to_app to match the updates we've made in https://docs.flutter.dev/add-to-app/ios/add-flutter-screen

[sethladd]

cc @hellohuanlin as we were just talking about this. No coding action needs to be taken right now. However, would you be willing to confirm that I articulated the "problem statement" correctly?

[sethladd]

fyi @jmagman