Docs: Specify missing global variables used in wp_print_theme_file_tree().

The `$relative_file` and `$stylesheet` variables are used in the `wp_print_theme_file_tree()` function but were not noted within the inline documentation.

Props mukesh27, desrosj,
Fixes #43682.

git-svn-id: https://develop.svn.wordpress.org/trunk@44477 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/misc.php

@@ -313,6 +313,10 @@ function wp_make_theme_file_tree( $allowed_files ) {
  * @since 4.9.0
  * @access private
  *
+ * @global string $relative_file Name of the file being edited relative to the
+ *                               theme directory.
+ * @global string $stylesheet    The stylesheet name of the theme being edited.
+ *
  * @param array|string $tree  List of file/folder paths, or filename.
  * @param int          $level The aria-level for the current iteration.
  * @param int          $size  The aria-setsize for the current iteration.