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/debugger.cc b/runtime/debugger.cc
index 1bdb0fc..a7feeef 100644
--- a/runtime/debugger.cc
+++ b/runtime/debugger.cc
@@ -1743,7 +1743,7 @@
       return field_value;
 
     case Primitive::kPrimNot:
-      field_value.SetL(f->GetObject(o).Decode());
+      field_value.SetL(f->GetObject(o).Ptr());
       return field_value;
 
     case Primitive::kPrimVoid: