Docs: Add missing descriptions for the $wpdb global in DocBlocks all the places.

See #32246.

Built from https://develop.svn.wordpress.org/trunk@35170


git-svn-id: http://core.svn.wordpress.org/trunk@35136 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/template-functions.php

@@ -568,7 +568,7 @@ function _list_meta_row( $entry, &$count ) {
  *
  * @since 1.2.0
  *
- * @global wpdb $wpdb
+ * @global wpdb $wpdb WordPress database abstraction object.
  *
  * @param WP_Post $post Optional. The post being edited.
  */
@@ -758,7 +758,7 @@ function page_template_dropdown( $default = '' ) {
  * @since 1.5.0
  * @since 4.4.0 `$post` argument was added.
  *
- * @global wpdb $wpdb
+ * @global wpdb $wpdb WordPress database abstraction object.
  *
  * @param int         $default Optional. The default page ID to be pre-selected. Default 0.
  * @param int         $parent  Optional. The parent page ID. Default 0.