Docs: Add missing description for $wpdb, $wp_db_version, and $wp_current_db_version globals.

Props mukesh27, utsav72640, immeet94, SergeyBiryukov.
See #45604.

git-svn-id: https://develop.svn.wordpress.org/trunk@45734 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme.php

@@ -3260,10 +3260,11 @@ function is_customize_preview() {
  * @access private
  * @see wp_delete_auto_drafts()
  *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
  * @param string   $new_status Transition to this post status.
  * @param string   $old_status Previous post status.
  * @param \WP_Post $post       Post data.
- * @global wpdb $wpdb
  */
 function _wp_keep_alive_customize_changeset_dependent_auto_drafts( $new_status, $old_status, $post ) {
 	global $wpdb;