update snippets to flutter 3

[ghost]

currently the snippets don't seem to leverage flutter 3 features

e.g.:statelessW

• expected result

class name extends StatelessWidget {
  const name({super.key});

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

• actual result

class name extends StatelessWidget {
  const name({Key? key}) : super(key: key);

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

[deandreamatias]

Implement compatibility with different major Flutter versions will be nice (related with #41) . Maybe a property config

[Nash0x7E2]

Plugin is now updated for v3 => https://marketplace.visualstudio.com/items?itemName=Nash.awesome-flutter-snippets