ART: Add dex::TypeIndex

Add abstraction for uint16_t type index.

Test: m test-art-host
Change-Id: I47708741c7c579cbbe59ab723c1e31c5fe71f83a
diff --git a/runtime/reflection.cc b/runtime/reflection.cc
index 3128380..8446b52 100644
--- a/runtime/reflection.cc
+++ b/runtime/reflection.cc
@@ -363,7 +363,7 @@
   Thread* const self = Thread::Current();
   PointerSize pointer_size = Runtime::Current()->GetClassLinker()->GetImagePointerSize();
   for (uint32_t i = 0; i < num_params; i++) {
-    uint16_t type_idx = params->GetTypeItem(i).type_idx_;
+    dex::TypeIndex type_idx = params->GetTypeItem(i).type_idx_;
     ObjPtr<mirror::Class> param_type(m->GetClassFromTypeIndex(type_idx,
                                                               true /* resolve*/,
                                                               pointer_size));