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_app.c

@@ -46,6 +46,7 @@
 #include "BLI_utildefines.h"
 #include "BLI_path_util.h"
 
+#include "BKE_appdir.h"
 #include "BKE_blender.h"
 #include "BKE_global.h"
 #include "structseq.h"