Creating iOS method channels changes after migrating to UIScene

### Page URL

https://docs.flutter.dev/platform-integration/platform-channels#step-4-add-an-ios-platform-specific-implementation

### Page source

_No response_

### Describe the problem

UIScene was introduced in Flutter 3.38 behind a feature flag, but is now the default in Flutter 3.41. After migrating to UIScene, developers need to create method channels in their AppDelegate's `didInitializeImplicitFlutterEngine` instead of `application:didFinishLaunchingWithOptions`.

See step 2 in https://docs.flutter.dev/release/breaking-changes/uiscenedelegate#migrate-appdelegate

### Expected fix

The docs should reflect the correct place to create method channels when using UIScene and potentially urge people to migrate to UIScene if they have not already

### Additional context

_No response_

### I would like to fix this problem.

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