Clarify return_tensor and return_text parameters
This PR fixes #20615 by clarifying that setting `return_tensors=True` will not return the decoded text, and you can't get a combination of `generated_text` and `generated_token_ids`.
_The documentation is not available anymore as the PR was closed or merged._<|||||>> LGTM thanks! @Narsil maybe a clear `ValueError` could be raised when sanitizing parameters when both `return_text` and `return_tensors` are `True`?

https://github.com/huggingface/transformers/pull/20729