[ZeroRedundancyOptimizer] Buckets as tensor view + minimize public interface (#52987)
Summary:
Updated version following https://github.com/pytorch/pytorch/issues/52764 (including comments from Shen), but this one I expect to be able to land.
ZeroRedundancyOptimizer:
- bucket as tensor views, optional
- make a lot of attributes private
- minor unit test refactor
- adding coverage in the unit test for with and without bucket views
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52987
Reviewed By: mrshenli
Differential Revision: D26728851
Pulled By: blefaudeux
fbshipit-source-id: f8c745966719c9076c20a554ef56198fb838856c
