Docs: Further type corrections and improvements for various docblocks.

See #53399


git-svn-id: https://develop.svn.wordpress.org/trunk@51302 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/media.php

@@ -715,7 +715,7 @@ function get_upload_iframe_src( $type = null, $post_id = null, $tab = null ) {
  *
  * @since 2.5.0
  *
- * @return mixed void|object WP_Error on failure
+ * @return null|array|void Array of error messages keyed by attachment ID, null or void on success.
  */
 function media_upload_form_handler() {
 	check_admin_referer( 'media-form' );