ART: IWYU handle_scope

Move wrappers to their own header. Forward-declare handles.

Bug: 119869270
Test: m
Change-Id: I9fba4df9b589cec07c7f687791ddbed81d188410
diff --git a/runtime/thread.h b/runtime/thread.h
index 334e9b7..4ac0f00 100644
--- a/runtime/thread.h
+++ b/runtime/thread.h
@@ -32,6 +32,7 @@
 #include "base/locks.h"
 #include "base/macros.h"
 #include "base/safe_map.h"
+#include "base/value_object.h"
 #include "entrypoints/jni/jni_entrypoints.h"
 #include "entrypoints/quick/quick_entrypoints.h"
 #include "handle_scope.h"