Docs: Add a @global entry for $wp_widget_factory in WP_Customize_Widgets::get_selective_refreshable_widgets().

Props jankimoradiya.
Fixes #41243.

git-svn-id: https://develop.svn.wordpress.org/trunk@41002 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-widgets.php

@@ -145,6 +145,8 @@ final class WP_Customize_Widgets {
 	 * @since 4.5.0
 	 * @access public
 	 *
+	 * @global WP_Widget_Factory $wp_widget_factory
+	 *
 	 * @return array Mapping of id_base to support. If theme doesn't support
 	 *               selective refresh, an empty array is returned.
 	 */