[Utils] add utilities for checking if certain utilities are properly documented

[sayakpaul]

What does this PR do?

We have a bunch of attention processors, normalization layers, and activation layers in the codebase and they have thin documentation. This is fine because users can always see their usage in the context of a model or a pipeline to get the fuller picture.

But since we document them in separate pages too, (such as this, this, and this), I think it makes sense to ensure these docs properly reflect what all we support.

This PR adds utilities to do that. @stevhliu I think you will like it :-)

[sayakpaul]

@stevhliu any idea why the doc build fails?

[stevhliu]

I'm not sure, the formatting all looks correct to me but for reason autodoc.py can't find them! cc @mishig25 have you encountered this before?

[sayakpaul]

@mishig25 a gentle ping.

[mishig25]

let me check

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[sayakpaul]

@stevhliu @yiyixuxu this is ready for review.

[sayakpaul]

Gentle ping @yiyixuxu.

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the contributing guidelines are likely to be ignored.