Adding [T5/MT5/UMT5]ForTokenClassification
Author: hackyon
Pull request: yes

# What does this PR do?

Adding [T5/MT5/UMT5]ForTokenClassification. See discussion [here](https://github.com/huggingface/transformers/pull/26683#issuecomment-1874899361).


## 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?
- [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/main/docs), and [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [x] 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.

@ArthurZucker

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @pacman100

Integrations:

- deepspeed: HF Trainer/Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc and @younesbelkada

Documentation: @stevhliu and @MKhalusova

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
- TensorFlow: @Rocketknight1

 -->


Comments:
Thanks @ArthurZucker. 

The CIs are green now. Please take a look when you get a chance. Thanks!

Yes! Will review 🤗 

Just rebasing the changes on top of the latest head

Thanks for adding the tests! It seems to have caused you a lot of extra work 😓 so let' s keep it as is. A lot of tests were missing


Thanks. 

Ran all 3 edited tests locally with RUN_SLOW=1 and they all passed. Also rebased off of main and re-pushed to do another run of CI checks

Test failure from tests_exotic_models seems unrelated:

E   Failed to import NATTEN's CPP backend. This could be due to an invalid/incomplete install. Please uninstall NATTEN (pip uninstall natten) and re-install with the correct torch build: shi-labs.com/natten

ERROR tests/models/dinat/test_modeling_dinat.py - RuntimeError: Failed to import transformers.models.dinat.modeling_dinat because of the following error (look up to see its traceback):
ERROR tests/models/nat/test_modeling_nat.py - RuntimeError: Failed to import transformers.models.nat.modeling_nat because of the following error (look up to see its traceback):

If we need the tests to pass, I can do another merge to upstream and re-push to trigger another test run.

Don't worry it is unrelated! 🤗  we can merge without 

> this might slow the CI a tad bit 😉

because of the new model classes (which is of course fine) or anything else?


Copied from of the full test suite of T5!