Editor: Add block theme infrastructure

Adds the required infrastructure to render block-based themes. This is sourced
from the Gutenberg plugin.

Fixes #54335.
Props bernhard-reiter, youknowriad, ntsekouras, hellofromtonya.


git-svn-id: https://develop.svn.wordpress.org/trunk@52062 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/taxonomy.php

@@ -18,6 +18,7 @@
  * avoid registering rewrite rules before the {@see 'init'} action.
  *
  * @since 2.8.0
+ * @since 5.9.0 Added `'wp_template_part_area'` taxonomy.
  *
  * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
  */
@@ -175,7 +176,7 @@ function create_initial_taxonomies() {
 
 	register_taxonomy(
 		'wp_theme',
-		array( 'wp_template', 'wp_global_styles' ),
+		array( 'wp_template', 'wp_template_part', 'wp_global_styles' ),
 		array(
 			'public'            => false,
 			'hierarchical'      => false,
@@ -191,6 +192,25 @@ function create_initial_taxonomies() {
 			'show_in_rest'      => false,
 		)
 	);
+
+	register_taxonomy(
+		'wp_template_part_area',
+		array( 'wp_template_part' ),
+		array(
+			'public'            => false,
+			'hierarchical'      => false,
+			'labels'            => array(
+				'name'          => __( 'Template Part Areas' ),
+				'singular_name' => __( 'Template Part Area' ),
+			),
+			'query_var'         => false,
+			'rewrite'           => false,
+			'show_ui'           => false,
+			'_builtin'          => true,
+			'show_in_nav_menus' => false,
+			'show_in_rest'      => false,
+		)
+	);
 }
 
 /**