Add caching to WP_Theme_JSON_Resolver_Gutenberg::get_user_data_from_custom_post_type()

[xknown]

Refactor
WP_Theme_JSON_Resolver_Gutenberg::get_user_data_from_custom_post_type
to add caching to the wp_global_styles post type lookup, and also to
remove the duplicate code added in
gutenberg_add_active_global_styles_link.

Fixes #36574

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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).

[github-actions]

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[Mamaduka]

Thanks for working on this, @xknown.

The code looks good to me. Let's rebase on the current trunk and merge this once all checks are green.

[xknown]

Thanks for working on this, @xknown.

The code looks good to me. Let's rebase on the current trunk and merge this once all checks are green.

Thanks for the review/feedback. I rebased the PR branch.

[Mamaduka]

Thank you, @xknown.

[github-actions]

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Kudos!

[youknowriad]

Is this something that need to be backported in core for 5.9? cc @oandregal @jorgefilipecosta

[noahtallen]

A heads up that I cherry-picked this into the gutenberg 12.0.1 point release.

[noisysocks]

If we don't backport it then it will be deleted when Gutenberg requires WP 5.9 at minimum, no?

[youknowriad]

The changes in lib/compat/wordpress-5.9/ yes. We should be more strict with changes made to lib/compat if we do want to make changes there without back porting, we need to move the changes to lib/compat/wordpress-6.0

[oandregal]

@youknowriad Without having looked deeply into the code, I'd think it's best to do it, yes: it changes some public method we're merging in 5.9 for the first time. While it is from a "private/internal" class, I'd rather play it safe.