auto_route support & class decorators

[Nolat]

Is your feature request related to a problem? Please describe.
I'm using the auto_route package, which needs to add an @RoutePage() decorator above the classes. If I try to add it above a functional widget, the generation doesn't work.

@RoutePage()
class SplashPage extends HookWidget {
  const SplashPage();

  @override
  Widget build(BuildContext context) {
    return Scaffold();
  }
}

Describe the solution you'd like
We need a way to add a decorator to the generated class.

@FunctionalWidget(
  decorators: [
    RoutePage
  ],
)
Widget splashPage() {
  return Scaffold();
}

[dickermoshe]

@rrousselGit
Should I spend time adding this, or is the macro version of this going to fix this issue?

[rrousselGit]

Feel free to make a PR yes