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/summarization.md

@@ -223,7 +223,7 @@ Hugging Face 계정에 로그인하면 모델을 업로드하고 커뮤니티에
 ...     args=training_args,
 ...     train_dataset=tokenized_billsum["train"],
 ...     eval_dataset=tokenized_billsum["test"],
-...     tokenizer=tokenizer,
+...     processing_class=tokenizer,
 ...     data_collator=data_collator,
 ...     compute_metrics=compute_metrics,
 ... )