Add @static* annotations where they are missing.

Initialize all static vars that are not, most to `null`.

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32650 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/media.php

@@ -535,6 +535,8 @@ document.body.className = document.body.className.replace('no-js', 'js');
  *
  * @global int $post_ID
  *
+ * @staticvar int $instance
+ *
  * @param string $editor_id
  */
 function media_buttons($editor_id = 'content') {