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/test/543-env-long-ref/env_long_ref.cc b/test/543-env-long-ref/env_long_ref.cc
index cd127ef..ce5602f 100644
--- a/test/543-env-long-ref/env_long_ref.cc
+++ b/test/543-env-long-ref/env_long_ref.cc
@@ -43,7 +43,7 @@
       uint32_t value = 0;
       CHECK(GetVReg(m, 1, kReferenceVReg, &value));
       CHECK_EQ(reinterpret_cast<mirror::Object*>(value),
-               soa_.Decode<mirror::Object>(expected_value_).Decode());
+               soa_.Decode<mirror::Object>(expected_value_).Ptr());
     }
     return true;
   }