Docs: Add missing description for a few globals in the admin.

This affects:

* `$post_type`
* `$post_type_object`
* `$taxonomy`
* `$title`
* `$wp_meta_boxes`

Follow-up to [31121], [32642], [32643], [37890], [43815], [44244], [45742], [53060], [53061], [54831].

Props shub07, 1naveengiri, sabernhardt, SergeyBiryukov.
Fixes #59561.
Built from https://develop.svn.wordpress.org/trunk@58419


git-svn-id: http://core.svn.wordpress.org/trunk@57868 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/plugin.php

@@ -2030,7 +2030,7 @@ function get_admin_page_parent( $parent_page = '' ) {
  *
  * @since 1.5.0
  *
- * @global string $title
+ * @global string $title       The title of the current screen.
  * @global array  $menu
  * @global array  $submenu
  * @global string $pagenow     The filename of the current screen.