[jit] register distributed backward (#38494)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38494
This register distributed.autograd.backward to jit
Test Plan: Imported from OSS
Differential Revision: D21596133
Pulled By: wanchaol
fbshipit-source-id: b64343010616a636304de54ae74ad4fb83445a62
