Add missing doc blocks to wp-admin/includes/*.

Fix some egregious uses of tabbing.
Some functions can simply return `apply_filters(...)` instead of setting a variable that is immediately returned.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32654 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/widgets.php

@@ -54,6 +54,8 @@ function wp_list_widgets() {
  *
  * @since 3.1.0
  * @access private
+ *
+ * @return int
  */
 function _sort_name_callback( $a, $b ) {
 	return strnatcasecmp( $a['name'], $b['name'] );