[WIP] migrate scatter_ to ATen CPU (+multithreading, nondeterministic) (#33139)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/24757, partially https://github.com/pytorch/pytorch/issues/33094. Uses fix introduces in https://github.com/pytorch/pytorch/issues/33108 to avoid regressions for some compilers.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33139
Differential Revision: D19882462
Pulled By: ngimel
fbshipit-source-id: 5016f186a4aadc3cc32edcfd9abdea11786f27e9
