Trainer - deprecate tokenizer for processing_class (#32385)

* Trainer - deprecate tokenizer for processing_class

* Extend chage across Seq2Seq trainer and docs

* Add tests

* Update to FutureWarning and add deprecation version

docs/source/ko/tasks/audio_classification.md

@@ -235,7 +235,7 @@ MinDS-14 데이터 세트의 샘플링 속도는 8000khz이므로(이 정보는
 ...     args=training_args,
 ...     train_dataset=encoded_minds["train"],
 ...     eval_dataset=encoded_minds["test"],
-...     tokenizer=feature_extractor,
+...     processing_class=feature_extractor,
 ...     compute_metrics=compute_metrics,
 ... )
 
@@ -321,4 +321,4 @@ For a more in-depth example of how to finetune a model for audio classification,
 'cash_deposit'
 ```
 </pt>
-</frameworkcontent>
+</frameworkcontent>