Support PEP 563 for HfArgumentParser
# What does this PR do?

Fixes #15739, support for [PEP 563](https://www.python.org/dev/peps/pep-0563/) is added, making it possible to write `from __future__ import annotations` in the file of dataclasses for `HfArgumentParser`. But this will not be available for Python with a version lower than 3.7, thus adding `from __future__ import annotations` in the test is currently infeasible because `__future__` imports should always occur at the beginning of the file. Instead, I write a test case with string literal annotations.

## 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?
- [x] Did you write any new necessary tests?


## Who can review?
@LysandreJik 

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15795). All of your documentation changes will be reflected on that endpoint.<|||||>@LysandreJik Hello, would be great if you could help or ask someone to give any feedback on this, thanks!
Seems #15951 updated the parser as well (just resolved the conflict), I've done the same work, and added a comment at the corresponding changing line.<|||||>Looking forward to any feedback.<|||||>Thanks for the ping! @sgugger could you give this a quick look? It's similar to the work merged in https://github.com/huggingface/transformers/pull/15951<|||||>It looks like you did a rebase on your PR that GitHub did not appreciate (the diff shows 292 files). Could you close this PR and open a fresh one?<|||||>@sgugger Github encountered some internal error a little while ago, it seems to be fine now.<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>@sgugger Thanks so much for the feedback! I've adopted that. In addition, I've replaced `... != type(None)` with `isinstance` to pass the quality check.<|||||>Cool, thanks again for your contribution!