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

examples/pytorch/multiple-choice/run_swag.py

@@ -440,7 +440,7 @@ def main():
         args=training_args,
         train_dataset=train_dataset if training_args.do_train else None,
         eval_dataset=eval_dataset if training_args.do_eval else None,
-        tokenizer=tokenizer,
+        processing_class=tokenizer,
         data_collator=data_collator,
         compute_metrics=compute_metrics,
     )