Refactor: BLI_path_util (split out app directory access)

This module is intended for path manipulation functions
but had utility functions added to access various directories.

source/blender/editors/space_file/space_file.c

@@ -41,6 +41,7 @@
 
 #include "BLO_readfile.h"
 
+#include "BKE_appdir.h"
 #include "BKE_context.h"
 #include "BKE_screen.h"
 #include "BKE_global.h"