Add type hints for ProphetNet (Pytorch) (#17223)
* added type hints to prophetnet
* reformatted with black
* fix bc black misformatted some parts
* fix imports
* fix imports
* Update src/transformers/models/prophetnet/configuration_prophetnet.py
Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>
* update OPTIONAL type hint and docstring
Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>
