This command should:

1. Determine if the correct directory is a plugin directory, throw if not
2. If the current plugin is using the old pubspec format, throw an error and guide users to the new pubspec format migration instruction on flutter.dev
3. Add platform specific folder and pubspec entries based on the platforms specified in --platforms flag.
4. A no-op iOS folder still needs to be present for this change. We need to remove the iOS folder as soon as 1.20 is released.

#59787