Tensorflow variant of DataCollatorForLanguageModeling.
Co-authored-by: Dalton Walker <dalton_walker@icloud.com>

# What does this PR do?

We didn't see any support for TensorFlow within the DataCollatorForLanguageModeling data class. Integrating directly with TensorFlow seems useful for TensorFlow users and avoids the necessity for tensor conversion.

This PR adds a TFDataCollatorForLangaugeModeling data class that integrates directly with TensorFlow tensors and paves the way for further TFDataCollator conversions. 


## Before submitting

- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [x] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?


## Who can review?

@LysandreJik 

Anyone in the community is free to review the PR.

Hello, it seems there are a lot of changes in your PR. If you think this isn't the case, do you mind closing this and opening a new PR so that we may see the correct diff? Also feel free to ping @Rocketknight1 and @sgugger for review<|||||>Will do! We had some issues with git but we can clean it up and resubmit.