Add ConvNeXT (#15277)
* First draft
* Add conversion script
* Improve conversion script
* Improve docs and implement tests
* Define model output class
* Fix tests
* Fix more tests
* Add model to README
* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
* Apply more suggestions from code review
* Apply suggestions from code review
* Rename dims to hidden_sizes
* Fix equivalence test
* Rename gamma to gamma_parameter
* Clean up conversion script
* Add ConvNextFeatureExtractor
* Add corresponding tests
* Implement feature extractor correctly
* Make implementation cleaner
* Add ConvNextStem class
* Improve design
* Update design to also include encoder
* Fix gamma parameter
* Use sample docstrings
* Finish conversion, add center cropping
* Replace nielsr by facebook, make feature extractor tests smaller
* Fix integration test
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
