separate QualifiedName into its own file (#19566)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19566
ghimport-source-id: c237f2a25d1aa9fc41f19fefe7a08a53a54279db
Differential Revision: D15032205
Reviewed By: shannonzhu
Pulled By: suo
fbshipit-source-id: 7527d97565559ebfb2556600eea5d93c1e141ac8
