ART: Refactor bit_utils and stl_util

Move iterator code from bit_utils.h into bit_utils_iterator.h. Move
Identity into stl_util_identity.h. Remove now unnecessary includes,
and fix up transitive users.

Test: m
Change-Id: Id1ce9cda66827c5d00584f39ed310b6b37629906
diff --git a/compiler/utils/arm/assembler_arm_vixl.cc b/compiler/utils/arm/assembler_arm_vixl.cc
index 6afc3dd..eb3f870 100644
--- a/compiler/utils/arm/assembler_arm_vixl.cc
+++ b/compiler/utils/arm/assembler_arm_vixl.cc
@@ -18,6 +18,8 @@
 #include <type_traits>
 
 #include "assembler_arm_vixl.h"
+#include "base/bit_utils.h"
+#include "base/bit_utils_iterator.h"
 #include "entrypoints/quick/quick_entrypoints.h"
 #include "thread.h"