tokenizer.batch_encoder_plus do not return input_len
# 🚀 Feature request

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     Please provide a link to the paper and code in case they exist. -->


```
 batch_tokens = self.tokenizer.batch_encode_plus(
                [example.text_a for example in examples],
                max_length=max_seq_len,
                pad_to_max_length=True,
            )
            for ex_id, (input_ids, segment_ids, input_mask) in enumerate(zip(batch_tokens["input_ids"],
                                                                             batch_tokens["token_type_ids"],
                                                                             batch_tokens["attention_mask"])):
                input_len = sum(1 for id in input_ids if id != self.tokenizer.pad_token_id)
```

if return input_len, it will be great.

## Motivation

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     related to a problem? e.g., I'm always frustrated when [...]. If this is related
     to another GitHub issue, please link here too. -->

## Your contribution

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
