Support graphs which return get_attr nodes directly as output (#107610)
Summary: Currently serializing graphs which return get_attr's directly as output fails. This diff adds support for that only in EXIR serializer while we still support unlifted params.
Test Plan: Added test case.
Differential Revision: D48258552
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107610
Approved by: https://github.com/angelayi
