Resolve SVG through Icon Registry - #82062

What?

• Closes Allow Core blocks to resolve internal UI SVGs through the Icon Registry #81225
• Core blocks now resolve their internal UI icons through the WordPress Icon Registry instead of hardcoding inline SVGs.
• Themes can override any block UI icon by registering a replacement SVG for a stable semantic identifier.
• Core retains its exact existing SVGs as defaults — no visual regression.

Why?

• Themes that need to replace Core block UI icons (e.g. to match a custom icon font like Material Symbols) currently must hide the hardcoded SVGs via CSS hacks and recreate them with ::before pseudo-elements.
• Some workarounds target SVG path data in CSS selectors, which break if Core updates an SVG.
• The Icon Registry already exists as a theming seam, but Core block UI icons don't use it yet.

How?

Exposed icon identifiers for theme override:

Key implementation details:

1. Extended the SVG sanitizer to allow stroke, stroke-width, stroke-linecap, stroke-linejoin, and fill attributes — needed for the stroked submenu chevron.
2. Registered core/navigation-submenu and core/navigation-menu-toggle via inline content in gutenberg_register_default_icons() since their SVGs don't fit the icon library's 24×24 / fill="currentColor" convention.
3. Made core/close public in the icon manifest.
4. Updated PHP render callbacks to call wp_get_icon() with fallback to the original hardcoded SVG.
5. Updated editor JS components to use a new useIcon() hook that fetches icons from the registry via core-data, with fallback to the original React SVGs.

Theme override example:

add_action( 'init', function () {
    wp_unregister_icon( 'core/search' );
    wp_register_icon( 'core/search', array(
        'label'   => 'Search',
        'content' => '<svg viewBox="0 0 24 24"><path d="..." /></svg>',
    ) );
}, 20 );

Works in both editor and frontend.

Testing Instructions

1. Add the snippet below to a theme's functions.php:

add_action( 'init', function () {
    wp_unregister_icon( 'core/search' );
    wp_register_icon( 'core/search', array(
        'label'   => 'Search',
        'content' => '<svg viewBox="0 0 24 24"><path d="M0 0 L24 24 M24 0 L0 24" stroke="currentColor" stroke-width="2"/></svg>',
    ) );
}, 20 );

2. Add a Search block with "Use icon button" enabled → custom SVG appears on frontend and editor.
3. Remove the override → default search icon is restored.
4. Run automated tests: npm run wp-env-test run -- phpunit --filter Tests_Blocks_Render_Icons

Use of AI Tools

This PR was implemented with assistance from GLM-5.2 via Ollama (ollama/glm-5.2:cloud).