Improve DETR post-processing methods
# What does this PR do?
- Adds `post_process_object_detection`, `post_process_semantic_segmentation`, `post_process_instance_segmentation` and `post_process_panoptic_segmentation` methods with optional resizing and thresholding to filter out low probability predictions.

This PR is part of a larger effort to ensure post-processing methods have consistent naming, input arguments and output. Deprecation warnings are added to existing post-processing methods.

## 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.
- [ X] 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?


_The documentation is not available anymore as the PR was closed or merged._<|||||>@amyeroberts @sgugger thank you both for the feedback! Could you take a final look at the PR? If everything looks fine, I'll apply the same changes to MaskFormer and update the model cards.<|||||>> Thanks for working on this. As mentioned internally, don't hesitate to separate PRs in focused bits: here there could have been:
> 
> * one PR to quickly fix the comments
> * one PR to add the post processing to DETR
> * one PR for the deprecation warnings

Makes sense, I'll split my future PRs into smaller, issue-specific ones.

> Also wondering if we should target a lower version than v5 for the removal of the methods, since this is all a bit of an experimental API.

I agree, we can target a lower version for the removal of deprecated methods.