Docs: Document the `$wp_registered_sidebars` global in `wp_map_sidebars_widgets()`.

Follow-up to [41555].

Props shailu25.
See #60021.
Built from https://develop.svn.wordpress.org/trunk@57234


git-svn-id: http://core.svn.wordpress.org/trunk@56740 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-alpha-57233';
+$wp_version = '6.5-alpha-57234';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/widgets.php

@@ -1370,6 +1370,8 @@ function retrieve_widgets( $theme_changed = false ) {
  * @since 4.9.0
  * @since 4.9.2 Always tries to restore widget assignments from previous data, not just if sidebars needed mapping.
  *
+ * @global array $wp_registered_sidebars The registered sidebars.
+ *
  * @param array $existing_sidebars_widgets List of sidebars and their widget instance IDs.
  * @return array Mapped sidebars widgets.
  */