Editor: Fix missing frontend section presets output.

[jorgefilipecosta]

Backports PHP changes in WordPress/gutenberg#42124 to the core. Adds the missing mechanism to output frontend styles of block level presets to the core. Props mcsf, oandregal, dmsnell, draganescu.
See #56467.

Testing

Paste the following code on a post:

<!-- wp:group {"settings":{"blocks":{"core/social-links":{"color":{"palette":{"custom":[{"slug":"button-red","color":"red","name":"button red"},{"slug":"button-blue","color":"blue","name":"button blue"}]}}}},"color":{"palette":{"custom":[{"slug":"global-aquamarine","color":"aquamarine","name":"Global aquamarine"},{"slug":"global-pink","color":"pink","name":"Global Pink"}]}}}} -->
<div class="wp-block-group"><!-- wp:paragraph -->
<p>Leaf paragraph of inner group block.</p>
<!-- /wp:paragraph -->

<!-- wp:social-links {"iconBackgroundColor":"button-red","iconBackgroundColorValue":"red","showLabels":true} -->
<ul class="wp-block-social-links has-visible-labels has-icon-background-color"><!-- wp:social-link {"url":"w.org","service":"wordpress","label":"red"} /--></ul>
<!-- /wp:social-links -->

<!-- wp:social-links {"iconBackgroundColor":"button-blue","iconBackgroundColorValue":"blue","showLabels":true} -->
<ul class="wp-block-social-links has-visible-labels has-icon-background-color"><!-- wp:social-link {"url":"w.org","service":"wordpress","label":"blue"} /--></ul>
<!-- /wp:social-links -->

<!-- wp:paragraph {"backgroundColor":"global-aquamarine"} -->
<p class="has-global-aquamarine-background-color has-background">global-aquamarine</p>
<!-- /wp:paragraph -->

<!-- wp:paragraph {"backgroundColor":"global-pink"} -->
<p class="has-global-pink-background-color has-background">global-pink</p>
<!-- /wp:paragraph --></div>
<!-- /wp:group -->

Verify the front-end result is:

[jorgefilipecosta]

Committed in 2b1febd.

[ockham]

Unfortunately, this seems to cause a fatal when the current stable version of the Gutenberg plugin is enabled:

Warning: Declaration of WP_Theme_JSON_6_1::get_stylesheet($types = Array, $origins = NULL) should be compatible with WP_Theme_JSON::get_stylesheet($types = Array, $origins = NULL, $options = Array) in /var/www/src/wp-content/plugins/gutenberg/lib/compat/wordpress-6.1/class-wp-theme-json-6-1.php on line 630

@jorgefilipecosta Could you revert this for now? We need to figure out a way that's compatible with the GB plugin 🙂

[ockham]

Update: Jorge reverted this in decd946. Thank you!

He also mentioned that we'll need to coordinate landing this with a Gutenberg release that includes the updated function signature. I believe that's WordPress/gutenberg#42124.