Add TokenClassification for Mistral, Mixtral and Qwen2 (#29878)

* Add MistralForTokenClassification

* Add tests and docs

* Add token classification for Mixtral and Qwen2

* Save llma for token classification draft

* Add token classification support for Llama, Gemma, Persimmon, StableLm and StarCoder2

* Formatting

* Add token classification support for Qwen2Moe model

* Add dropout layer to each ForTokenClassification model

* Add copied from in tests

* Update src/transformers/models/llama/modeling_llama.py

Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Propagate suggested changes

* Style

---------

Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

docs/source/en/model_doc/gemma.md

@@ -60,6 +60,11 @@ This model was contributed by [Arthur Zucker](https://huggingface.co/ArthurZ), [
 [[autodoc]] GemmaForSequenceClassification
     - forward
 
+## GemmaForTokenClassification
+
+[[autodoc]] GemmaForTokenClassification
+    - forward
+
 ## FlaxGemmaModel
 
 [[autodoc]] FlaxGemmaModel