Docs: Add a @global entry for $post variable in wp_post_preview_js().

Props avinapatel.
Fixes #41194.
Built from https://develop.svn.wordpress.org/trunk@40959


git-svn-id: http://core.svn.wordpress.org/trunk@40809 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -5455,6 +5455,8 @@ function wp_delete_file( $file ) {
  * This prevents reusing the same tab for a preview when the user has navigated away.
  *
  * @since 4.3.0
+ *
+ * @global WP_Post $post
  */
 function wp_post_preview_js() {
 	global $post;