Updates `wp_render_elements_support()` to use the HTML API

[ntsekouras]

Replaces the RegEx and PHP string functionality in wp_render_elements_support() to use the new HTML API (WP_HTML_Tag_Processor).

Why?

This class was built to quickly and reliably modify HTML tag attributes. It circumvents specific problems, such as matching on the wrong attributes (such as data-custom-class="some value"), overlooking matches (such as class=blue or class='wp-block-group'), writing updates in a way that get overlooked by the browser (by writing to the end of the tag instead of before any potential duplicate attributes), and by writing invalid content to the HTML (such as through a bug in a PCRE pattern greedily matching more than it should).

Reference:

• ​Gutenberg PR 46625

Trac ticket: https://core.trac.wordpress.org/ticket/57642

Updates wp_render_elements_support to use the new html API.

Related GB PR: ​https://github.com/WordPress/gutenberg/pull/46625

[flixos90]

@ntsekouras Changing this to an enhancement as this isn't really a bug :)

I'm going to review this shortly, should be reasonable to commit today or tomorrow before the beta release; otherwise we may want to change it to a "task (blessed)".

[flixos90]

In 55235:

Editor: Use WP_HTML_Tag_Processor in wp_render_elements_support().

Props ntsekouras.
Fixes #57642.

Committed in https://core.trac.wordpress.org/changeset/55235.