refactor(dart version): Enable super parameters

[IlyaZadyabin]

Request to change sdk constraints to sdk: ">=2.17.0 <3.0.0". This will enable super parameters, which will:

1. Reduce circular_progress_builder.dart and linear_progress_builder.dart size drastically
2. Allow LinearProgressBuilder and CircularProgressBuilder parameters to be documented the same way as ProgressBuilder

[ayushin]

Sounds like a good idea to me.