

TITLE
Introduce `PartialState` as the device handler in the `Trainer`

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# What does this PR do?

This PR is the start of the `Trainer` integration of [Accelerate](https://github.com/huggingface/accelerate)

The integration will follow multiple stages to ensure small changes happen iteratively. This first one simply changes the device handler/setter to be the `PartialState` in `Accelerate` and nothing more. In a follow-up PR, I will start to include more utilities utilizing it.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/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.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@sgugger @pacman100 
