Remove object_utils.h.

Break into object_lock, field_helper and method_helper.
Clean up header files following this.
Also tidy some of the Handle code in response to compiler errors when resolving
the changes in this CL.

Change-Id: I73e63015a0f02a754d0866bfaf58208aebcaa295
diff --git a/runtime/class_linker_test.cc b/runtime/class_linker_test.cc
index 7930b48..21fe006 100644
--- a/runtime/class_linker_test.cc
+++ b/runtime/class_linker_test.cc
@@ -23,6 +23,7 @@
 #include "common_runtime_test.h"
 #include "dex_file.h"
 #include "entrypoints/entrypoint_utils-inl.h"
+#include "field_helper.h"
 #include "gc/heap.h"
 #include "mirror/art_field-inl.h"
 #include "mirror/art_method.h"