Summary:
Class FQN is needed when unpacking CustomObj instance.
For all other Arguments, e.g. Tensor, TensorList, SymInt, we always know their exact type. However, CustomObjArgument had an opaque type.
Adding this field also helps unveiling the type of this opaque object.
Test Plan: CI
Differential Revision: D53029847
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118158
Approved by: https://github.com/zhxchen17