Auto processor (#14465)
* Add AutoProcessor class
* Init and tests
* Add doc
* Fix init
* Update src/transformers/models/auto/processing_auto.py
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
* Reverts to tokenizer or feature extractor when available
* Adapt test
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
