Add WavLM (#14354)

* first commit

* fix some stuff

* fix more readme

* Apply suggestions from code review

* update

* correct

* up

* attn layer works

* push code

* make modedls work

* Small change

* more refactor

* finish

* up

* fix convertsion

* fix position bias

* Fix style

* fix conversion

* make fix-copies

* add

* clean

* fix docs

* fix

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* apply final changes

* make fix-copies

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/_toctree.yml

@@ -284,6 +284,8 @@
       title: VisualBERT
     - local: model_doc/wav2vec2
       title: Wav2Vec2
+    - local: model_doc/wavlm
+      title: WavLM
     - local: model_doc/xlm
       title: XLM
     - local: model_doc/xlmprophetnet