[WIP] Move torch.fx into its own target (#46658)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46658
ghstack-source-id: 115213192
Test Plan: waitforsadcastle
Reviewed By: zdevito, vkuzo
Differential Revision: D24374723
fbshipit-source-id: 2b5708001f5df2ffb21ea5e586e26030653ccdcf
