[Tokenizer Utils Base] Make pad function more flexible (#9928)

* change tokenizer requirement

* split line

* Correct typo from list to str

* improve style

* make other function pretty as well

* add comment

* correct typo

* add new test

* pass tests for tok without padding token

* Apply suggestions from code review

src/transformers/models/blenderbot_small/tokenization_blenderbot_small.py

@@ -92,7 +92,7 @@ class BlenderbotSmallTokenizer(PreTrainedTokenizer):
         },
     }
     max_model_input_sizes = {"facebook/blenderbot_small-90M": 512}
-    model_input_names = ["attention_mask"]
+    model_input_names = ["input_ids", "attention_mask"]
 
     def __init__(
         self,