Rename ObjPtr::Decode to ObjPtr::Ptr

Done to prevent ambiguity with ScopedObjectAccess::Decode.

Bug: 31113334

Test: test-art-host
Change-Id: I07a2497cc9cf66386311798933547471987fc316
diff --git a/runtime/reflection-inl.h b/runtime/reflection-inl.h
index d7db8a4..52cdfb8 100644
--- a/runtime/reflection-inl.h
+++ b/runtime/reflection-inl.h
@@ -107,7 +107,7 @@
   if (UNLIKELY(o == nullptr)) {
     ThrowNullPointerException("null receiver");
     return false;
-  } else if (UNLIKELY(!o->InstanceOf(c.Decode()))) {
+  } else if (UNLIKELY(!o->InstanceOf(c.Ptr()))) {
     InvalidReceiverError(o, c);
     return false;
   }