[WIP] Block Support: Add typography letter spacing

[ramonjd]

Description

This PR is currently WIP.

We're trying to add letter spacing support for block typography.

At the start, we've started with a value of true, but maybe we'd like to specify units, e.g.,

"__experimentalLetterSpacing": [ "px", "em", "rem" ], and "__experimentalLetterSpacing": true for all of them.

How has this been tested?

As we go for now.

To (experimental-)theme.json add:

"settings": {
    ...
    "typography": {
          ....
          "customLetterSpacing": true,
     }
}

and to block.json (e.g., in core/site-title or core/heading ):

"supports": {
    ....
    "__experimentalLetterSpacing": true,
}

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[ramonjd]

This is taken 1:1 from the line-height control component.

I think there could be scope to abstract/combine them, especially if we plan to freshen up the design of the sidebar controls (See #27331)

[carolinan]

There is already a PR for this, in which way does this version differ, and if there are problems with my version can you provide feedback? #31118

[ramonjd]

There is already a PR for this, in which way does this version differ, and if there are problems with my version can you provide feedback? #31118

Thanks @carolinan ! That'll teach me for not keeping an eye on current PRs. 😄
I think you're further along, especially with units etc. I'll close this one. Cheers!