idtt + zch distributed inference (#35763)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35763
Adds inference function and test for ScatterAssign
Test Plan: Updated unit test
Reviewed By: yyetim, shunting1986
Differential Revision: D20501079
fbshipit-source-id: 7ec6ef0127a151250dd699c90c2b80c35cfb1fe4
