Update BridgeTowerForContrastiveLearning
Author: abhiwand
Pull request: yes

# What does this PR do?

1. Use return_loss in BridgeTowerForContrastiveLearning
2. Update example in BridgeTowerForContrastiveLearning
3. Handles @amyeroberts suggestion from https://github.com/huggingface/transformers/pull/21964 to use smaller vocab_size for BridgeTowerTester

<!--
Congratulations! You've made it this far! You're not quite done yet though.

Once merged, your PR is going to appear in the release notes with the title you set, so make sure it's a great title that fully reflects the extent of your awesome contribution.

Then, please replace this with a description of the change and which issue is fixed (if applicable). Please also include relevant motivation and context. List any dependencies (if any) that are required for this change.

Once you're done, someone will review your PR shortly (see the section "Who can review?" below to tag some potential reviewers). They may suggest changes to make the code even better. If no one reviewed your PR after a week has passed, don't hesitate to post a new comment @-mentioning the same persons---sometimes notifications get lost.
-->

<!-- Remove if not applicable -->

Fixes # (issue)


## Before submitting
- [x] 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).
- [ ] 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.
@amyeroberts @sgugger can you please help review this fix. 
<!-- 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: @sgugger

Integrations:

- deepspeed: HF Trainer: @stas00, Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam

Documentation: @sgugger, @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: @sgugger
- TensorFlow: @Rocketknight1

 -->


Comments:
_The documentation is not available anymore as the PR was closed or merged._

Thank @ydshieh and @amyeroberts for your suggestions. In the latest commit, we addressed all of your feedbacks except one that regards to tests inspired from Clip's tests.
@ydshieh Regarding tests, yes, you are right, it will require more works. We plan to have another PR to improve tests (following your suggestion) soon, yet this is not the main purpose of this PR. We would love to have you help us working on this, we truly appreciate your offer to help. 
It will be great if you can help to merge this PR without restructuring tests, and please feel free to contact/tag me if you would like me to cooperate on improving/restructuring tests. 
Thanks

Thank @amyeroberts for approving this PR.
@ydshieh We have updated the 2 positions that you most recently suggested to change in the latest commit. Could you please review, approve, and merge the PR? 
We are looking forward to having this PR merged soon. 
Thanks a lot.
 

Thank you again, @tileintel  and @abhiwand, for the work! Merge now 🚀 !  

> and please feel free to contact/tag me if you would like me to cooperate on improving/restructuring tests. Thanks

Hi @tileintel. If you are willing and have time to work on the tests part, it would be really great. But as I mentioned earlier, we understand this part is not always the main interest of community contributors: as long as the basic necessary tests are added, it is sufficient for a model addition PR. So I can work on the test restructuring unless you would like to do it :-). WDYT?

> > and please feel free to contact/tag me if you would like me to cooperate on improving/restructuring tests. Thanks
> 
> Hi @tileintel. If you are willing and have time to work on the tests part, it would be really great. But as I mentioned earlier, we understand this part is not always the main interest of community contributors: as long as the basic necessary tests are added, it is sufficient for a model addition PR. So I can work on the test restructuring unless you would like to do it :-). WDYT?

@ydshieh thanks for pointing this out. We would really appreciate if you can work on restructuring tests. Thank you!

> > > and please feel free to contact/tag me if you would like me to cooperate on improving/restructuring tests. Thanks
> > 
> > 
> > Hi @tileintel. If you are willing and have time to work on the tests part, it would be really great. But as I mentioned earlier, we understand this part is not always the main interest of community contributors: as long as the basic necessary tests are added, it is sufficient for a model addition PR. So I can work on the test restructuring unless you would like to do it :-). WDYT?
> 
> @ydshieh thanks for pointing this out. We would really appreciate if you can work on restructuring tests. Thank you!

Sure, thanks for letting me know 😊