[ios]Make "add to SwiftUI app" doc up to date with iOS 18

[hellohuanlin]

Page URL

https://docs.flutter.dev/add-to-app/ios/add-flutter-screen/

Page source

No response

Describe the problem

The "Add to (SwiftUI) app" doc is outdated. For example, iOS 17 introduced macros which makes things like @EnvironmentObject outdated (we didn't update it last year). There may be other updates needed for iOS 18.

Moved from: https://github.com/flutter/flutter/issues/150945

Expected fix

No response

Additional context

No response

I would like to fix this problem.

• [X] I will try and fix this problem on docs.flutter.dev.