Add type hints for Pegasus model (PyTorch)
Adding type hints for forward methods in user-facing class for Pegasus model (PyTorch) as mentioned in #16059

@Rocketknight1 
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_16164). All of your documentation changes will be reflected on that endpoint.<|||||>it seems like BART model was not updated yet, hence the inconsistency<|||||>@Tegzes Unfortunately this will have to wait for the BART PR to avoid breaking repository consistency, but I'll take a look at that point!<|||||>@Rocketknight1  I saw that BART model was updated, along with multiple models depending on it, including this one. Should I close the PR?<|||||>Hi @Tegzes, there might still be portions of `modeling_pegasus.py` that need type hints - if you could check that and either submit a Pegasus PR or close this one that would be great. And sorry for the confusion caused by the copying dependencies!