Icons: Add a core-admin collection for the admin interface.

The icons the admin bar and the admin menu are meant to render live in the
`core` collection, so unregistering that collection to keep the default icon
set out of the Icon block would also wipe out every icon in the dashboard
chrome.

A new `admin` property in the icons manifest marks the icons the admin
interface renders. Those are registered in a `core-admin` collection in
addition to `core`, always as non-public icons there, so that the collection
contributes nothing to the icons REST API or to the Icon block.

The manifest is generated from `gutenberg/packages/icons` by
`grunt copy:icon-library-manifest`, so the `admin` flags arrive with the next
Gutenberg hash bump.

Backports WordPress/gutenberg#83261 to core.

Props wildworks.
See #66114.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: t-hamano

src/wp-includes/icons.php

@@ -44,10 +44,10 @@ function wp_unregister_icon_collection( $slug ) {
  * @since 7.2.0 Added the `public` property.
  *
  * @param string $icon_name Namespaced icon name in the form "collection/icon-name"
- *                          (e.g. "my-plugin/arrow-left"). The "core" collection is
- *                          reserved for WordPress core icons; third-party code should
- *                          register icons under its own collection rather than the
- *                          "core" collection.
+ *                          (e.g. "my-plugin/arrow-left"). The "core" and "core-admin"
+ *                          collections are reserved for WordPress core icons; third-party
+ *                          code should register icons under its own collection rather than
+ *                          a reserved one.
  * @param array  $args      {
  *     List of properties for the icon.
  *
@@ -94,11 +94,21 @@ function _wp_register_default_icon_collections() {
 			'description' => __( 'Default icon collection.' ),
 		)
 	);
+	wp_register_icon_collection(
+		'core-admin',
+		array(
+			'label'       => __( 'WordPress Admin' ),
+			'description' => __( 'Icon collection used by the WordPress admin interface.' ),
+		)
+	);
 }
 
 /**
  * Registers the default core icons from the manifest.
  *
+ * Icons flagged as `admin` in the manifest are also registered in the "core-admin"
+ * collection, always as non-public icons there.
+ *
  * @since 7.1.0
  * @access private
  */
@@ -114,17 +124,17 @@ function _wp_register_default_icons() {
 		return;
 	}
 
-	$collection = include $manifest_path;
+	$manifest = include $manifest_path;
 
-	if ( empty( $collection ) ) {
+	if ( empty( $manifest ) ) {
 		wp_trigger_error(
 			__FUNCTION__,
 			__( 'Core icon collection manifest is empty or invalid.' )
 		);
 		return;
 	}
 
-	foreach ( $collection as $icon_name => $icon_data ) {
+	foreach ( $manifest as $icon_name => $icon_data ) {
 		if (
 			empty( $icon_data['filePath'] )
 			|| ! is_string( $icon_data['filePath'] )
@@ -147,6 +157,11 @@ function _wp_register_default_icons() {
 		}
 
 		wp_register_icon( 'core/' . $icon_name, $icon_args );
+
+		if ( ! empty( $icon_data['admin'] ) ) {
+			$icon_args['public'] = false;
+			wp_register_icon( 'core-admin/' . $icon_name, $icon_args );
+		}
 	}
 }