Big cleanup of glue_convert_examples_to_features (#3688)

* Big cleanup of `glue_convert_examples_to_features`

* Use batch_encode_plus

* Cleaner wrapping of glue_convert_examples_to_features for TF

@lysandrejik

* Cleanup syntax, thanks to @mfuntowicz

* Raise explicit error in case of user error

examples/glue/run_pl_glue.py

@@ -63,12 +63,8 @@ class GLUETransformer(BaseTransformer):
                     examples,
                     self.tokenizer,
                     max_length=args.max_seq_length,
-                    task=args.task,
                     label_list=self.labels,
                     output_mode=args.glue_output_mode,
-                    pad_on_left=bool(args.model_type in ["xlnet"]),  # pad on the left for xlnet
-                    pad_token=self.tokenizer.convert_tokens_to_ids([self.tokenizer.pad_token])[0],
-                    pad_token_segment_id=self.tokenizer.pad_token_type_id,
                 )
                 logger.info("Saving features into cached file %s", cached_features_file)
                 torch.save(features, cached_features_file)