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/python/intern/bpy_interface.c

@@ -63,6 +63,7 @@
 
 #include "DNA_text_types.h"
 
+#include "BKE_appdir.h"
 #include "BKE_context.h"
 #include "BKE_text.h"
 #include "BKE_main.h"