Footnotes: Add typography, dimensions, and border block supports

[mikachan]

What?

This updates the block supports for the Footnotes block to include typography, dimensions, and border controls. It also adjusts the color supports so that link and text are the defaults, rather than background and text.

Why?

This gives the Footnotes block further design flexibility. Follow-on from #52897, and addresses this comment: #52897 (comment).

How?

Updates the Footnotes block.json file.

Testing Instructions

1. Open the Post Editor
2. Add some text
3. Highlight some text, use the drop down menu in the block toolbar to add a footnote
4. Open block settings for the footnote and ensure that there are typography, dimensions and border controls
5. Please try applying controls from the available options; make sure the settings are applied in the editor and the front end

Screenshots or screencast

Default settings for the Footnotes block with this PR:

[ndiego]

I have added this to the 6.3 Project Board. While we are very late in the release cycle, I believe the Footnotes block fundamentally needs these block supports. Since the Footnotes block is included for the first time in 6.3, we should try and provide the best user experience possible.

[MaggieCabrera]

Yes please, let's get these in with the block

[t-hamano]

My understanding is that after the Beta release, it becomes a feature freeze, and in principle, new features should not be able to be added. It pains me too that this feature is not available, but how about removing it from the 6.3 project board?

It might also be a good idea to add these added block supports to the table of each block support tied to the #43241 tracking issue.

[mikachan]

I'm going to merge this, as it's a follow-up to #52897 which will be included in GB 16.4, and it would be nice to also include this PR in 16.4 ✨

[mikachan]

I just cherry-picked this PR to the release/16.4 branch to get it included in the next release: 98fe154