Change unpacking of TF mpnet, rag, roformer inputs to use decorator
# What does this PR do?

As part of #16051 this PR changes the unpacking of the inputs of TF mpnet, rag, roformer to use the decorator instead.

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Fixes # (issue)


## 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/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] 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?

@Rocketknight1  @gante 

_The documentation is not available anymore as the PR was closed or merged._<|||||>These changes are also in #16112 -- can I close this PR? :)<|||||>Sorry about this mess.  I will close it<|||||>> Sorry about this mess. I will close it

No worries! Thank you for closing the PR