Add type hints for UniSpeech
Adding type hints for forward methods in user-facing class for UniSpeech as mentioned in #16059

@Rocketknight1 
_The documentation is not available anymore as the PR was closed or merged._<|||||>Hey, this looks good but I'm going to leave a final review until the `Wav2vec` issue is resolved - for the record, I think it's totally fine for you to update that file too!<|||||>Yeah, I think I will work on it and make a commit right away<|||||>There are some other models that are dependent on Wave2Vec2, I will modify them asap<|||||>@Rocketknight1  I think it's good to go now