Move AST utilities to a subdirectory

Move AST related utilities to compiler/translator/tree_util.

BUG=angleproject:2409
TEST=angle_unittests

Change-Id: I7567c2f6f2710292029263257c7ac26e2a144ac8
Reviewed-on: https://chromium-review.googlesource.com/966032
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/RemovePow.cpp b/src/compiler/translator/RemovePow.cpp
index b2cdac5..c5cab90 100644
--- a/src/compiler/translator/RemovePow.cpp
+++ b/src/compiler/translator/RemovePow.cpp
@@ -11,7 +11,7 @@
 #include "compiler/translator/RemovePow.h"
 
 #include "compiler/translator/InfoSink.h"
-#include "compiler/translator/IntermTraverse.h"
+#include "compiler/translator/tree_util/IntermTraverse.h"
 
 namespace sh
 {