Use mangled type names in `cc_struct_upcast_impl`'s `cast_fn_name`.

PiperOrigin-RevId: 471545380
diff --git a/rs_bindings_from_cc/ir.h b/rs_bindings_from_cc/ir.h
index b3eab93..5573849 100644
--- a/rs_bindings_from_cc/ir.h
+++ b/rs_bindings_from_cc/ir.h
@@ -576,6 +576,7 @@
   // `rs_name` is similar to "__CcTemplateInst8MyStructIiE").
   std::string rs_name;
   std::string cc_name;
+  std::string mangled_cc_name;
 
   ItemId id;
   BazelLabel owning_target;