[MMS] Scaling Speech Technology to 1,000+ Languages | Add attention adapter to Wav2Vec2 (#23813)

* add fine-tuned with adapter layer

* Add set_target_lang to tokenizer

* Implement load adapter

* add tests

* make style

* Apply suggestions from code review

* Update src/transformers/models/wav2vec2/tokenization_wav2vec2.py

* make fix-copies

* Apply suggestions from code review

* make fix-copies

* make style again

* mkae style again

* fix doc string

* Update tests/models/wav2vec2/test_tokenization_wav2vec2.py

* Apply suggestions from code review

* fix

* Correct wav2vec2 adapter

* mkae style

* Update src/transformers/models/wav2vec2/modeling_wav2vec2.py

Co-authored-by: Sanchit Gandhi <93869735+sanchit-gandhi@users.noreply.github.com>

* add more nice docs

* finish

* finish

* Apply suggestions from code review

Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Apply suggestions from code review

* all finish

---------

Co-authored-by: Sanchit Gandhi <93869735+sanchit-gandhi@users.noreply.github.com>
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

docs/source/en/_toctree.yml

@@ -543,6 +543,8 @@
         title: Hubert
       - local: model_doc/mctct
         title: MCTCT
+      - local: model_doc/mms
+        title: MMS
       - local: model_doc/sew
         title: SEW
       - local: model_doc/sew-d