[JIT] Factor out peephole to own test file (#50220)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50220
Test Plan: Imported from OSS
Reviewed By: tugsbayasgalan
Differential Revision: D25856263
Pulled By: eellison
fbshipit-source-id: f3d918d860e64e788e0bb9b9cb85125660f834c6
