Feature Request: Some generators

[alejandrogiubel]

Add some feats generators
https://pub.dev/packages/retrofit
https://pub.dev/packages/freezed
https://pub.dev/packages/riverpod_generator
https://pub.dev/packages/reactive_forms_generator

[Arjun544]

@alejandrogiubel thank you for the feedback.

The main reason I haven't added any generators yet is that using a templating approach in FlutterInit makes the generated code extremely difficult to write, maintain, and debug.

However, I do plan to add generators once FlutterInit reaches a stable version.