move code to rest-api.php file

lib/compat/wordpress-6.8/rest-api.php

@@ -49,3 +49,41 @@ function ( $taxonomy ) {
 		remove_filter( "rest_{$taxonomy}_query", 'gutenberg_respect_taxonomy_default_args_in_rest_api' );
 	}
 );
+
+/**
+ * Adds the default template part areas to the REST API index.
+ *
+ * This function exposes the default template part areas through the WordPress REST API.
+ * Note: This function backports into the wp-includes/rest-api/class-wp-rest-server.php file.
+ *
+ * @param WP_REST_Response $response REST API response.
+ * @return WP_REST_Response Modified REST API response with default template part areas.
+ */
+function gutenberg_add_default_template_part_areas_to_index( WP_REST_Response $response ) {
+	$response->data['default_template_part_areas'] = get_allowed_block_template_part_areas();
+	return $response;
+}
+
+add_filter( 'rest_index', 'gutenberg_add_default_template_part_areas_to_index' );
+
+/**
+ * Adds the default template types to the REST API index.
+ *
+ * This function exposes the default template types through the WordPress REST API.
+ * Note: This function backports into the wp-includes/rest-api/class-wp-rest-server.php file.
+ *
+ * @param WP_REST_Response $response REST API response.
+ * @return WP_REST_Response Modified REST API response with default template part areas.
+ */
+function gutenberg_add_default_template_types_to_index( WP_REST_Response $response ) {
+	$indexed_template_types = array();
+	foreach ( get_default_block_template_types() as $slug => $template_type ) {
+		$template_type['slug']    = (string) $slug;
+		$indexed_template_types[] = $template_type;
+	}
+
+	$response->data['default_template_types'] = $indexed_template_types;
+	return $response;
+}
+
+add_filter( 'rest_index', 'gutenberg_add_default_template_types_to_index' );