Global Styles: Use low-level cache for get_user_data_from_wp_global_styles

[mmtr]

Backports changes from WordPress/wordpress-develop#3517

See also #44946 and https://core.trac.wordpress.org/ticket/56901

Proposed changes

This change removes caching of global styles for logged in users, allowing "wp_global_styles" custom post type to be imported completely, regardless of any previously cached data. This change now relies on the lower-level native WP_Query cache invalidation methods for the global styles post type.

Testing Instructions

• Use Twenty Twenty Two (TT2) theme
• Use WordPress 6.0.3
• Log into the admin area
• Go to Appearance > Editor
• Open the Global Styles UI
• Select "Browse Styles"
• Select any non-default variation
• Select "Save" to save the new global styles
• Go back to the Dashboard
• Go to Tools > Export
• Click on "Download Export File" using "All content"
• Using another local site, with WordPress 6.1 RC3 (where the issue The Issue with demo import with WP 6.1 #44946 is still present) and Gutenberg running this branch
• Log into the admin area
• Go to Tools > Import
• Select "Install Now" for the "WordPress" importer
• Select "Run Importer"
• Select the XML file using "Choose File"
• Click on the "Upload file and import" button
• View site in the frontend
• Make sure the styles use the non-default variation you selected

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[oandregal]

Thanks for the PR!

This backports code that is in core, both in 6.1 and trunk. I've done some testing and it works fine: using style variations in both new sites (no wp_global_styles CPT) and old sites; changing themes; using WordPress 6.1 and 6.0 as base.

I was unable to reproduce the bug with import content in Gutenberg trunk (the issue that was raised in 6.1 RC3). This change is worth doing anyway.