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/ParseContext.cpp b/src/compiler/translator/ParseContext.cpp
index 0a01022..f0f9380 100644
--- a/src/compiler/translator/ParseContext.cpp
+++ b/src/compiler/translator/ParseContext.cpp
@@ -11,14 +11,13 @@
 
 #include "common/mathutil.h"
 #include "compiler/preprocessor/SourceLocation.h"
-#include "compiler/translator/BuiltIn_autogen.h"
 #include "compiler/translator/Declarator.h"
-#include "compiler/translator/IntermNode_util.h"
 #include "compiler/translator/ParseContext_autogen.h"
 #include "compiler/translator/StaticType.h"
 #include "compiler/translator/ValidateGlobalInitializer.h"
 #include "compiler/translator/ValidateSwitch.h"
 #include "compiler/translator/glslang.h"
+#include "compiler/translator/tree_util/IntermNode_util.h"
 #include "compiler/translator/util.h"
 
 namespace sh