Make WP_Theme::get_files() a general method for retrieving any file types, at...

Make WP_Theme::get_files() a general method for retrieving any file types, at any depth, optionally to include parent files. see #20546.



git-svn-id: https://core.svn.wordpress.org/trunk@20588 1a063a9b-81f0-0310-95a4-ce76da25c4cd