Move DataCollatorForMultipleChoice from the docs to the package (#34763)

* Add implementation for DataCollatorForMultipleChoice based on docs.

* Add DataCollatorForMultipleChoice to import structure.

* Remove custom DataCollatorForMultipleChoice implementations from example scripts.

* Remove custom implementations of DataCollatorForMultipleChoice from docs in English, Spanish, Japanese and Korean.

* Refactor torch version of DataCollatorForMultipleChoice to be more easily understandable.

* Apply suggested changes and run make fixup.

* fix copies, style and fixup

* add missing documentation

* nits

* fix docstring

* style

* nits

* isort

---------

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>
Co-authored-by: Arthur Zucker <arthur.zucker@gmail.com>

tests/trainer/test_trainer.py

@@ -687,7 +687,7 @@ class TrainerIntegrationCommon:
         keys = list(state_dict.keys())
 
         shard_files = [
-            shard_name.replace(f".{extension}", f"-{idx+1:05d}-of-{len(keys):05d}.{extension}")
+            shard_name.replace(f".{extension}", f"-{idx + 1:05d}-of-{len(keys):05d}.{extension}")
             for idx in range(len(keys))
         ]
         index = {"metadata": {}, "weight_map": {key: shard_files[i] for i, key in enumerate(keys)}}