Revert part of d9c4004cd9738d845066b99a6efa04e27c29c1cb

Brings back `::get_included_files()`, `::get_excluded_files()` & `::get_unreadable_files()` as they are used in unit tests
revert 3e213ac2bbd06d02383ed5290d6475cc1bed0c36 for now as it breaks standard installs with wp-config.php up one from root