Allow `Trainer.get_optimizer_cls_and_kwargs` to be overridden (#31875)

* Change `Trainer.get_optimizer_cls_and_kwargs` to `self.`

* Make `get_optimizer_cls_and_kwargs` an instance method

* Fixing typo

* Revert `get_optimizer_cls_and_kwargs` to staticmethod

* restore newline to trainer.py eof

src/transformers/trainer.py

@@ -1079,7 +1079,7 @@ class Trainer:
                 },
             ]
 
-            optimizer_cls, optimizer_kwargs = Trainer.get_optimizer_cls_and_kwargs(self.args, opt_model)
+            optimizer_cls, optimizer_kwargs = self.get_optimizer_cls_and_kwargs(self.args, opt_model)
 
             # Overwrite `params` in case it's created by `get_optimizer_cls_and_kwargs`
             # e.g. for GaLore optimizer.