Add experimental deterministic flag (#38683)
Summary:
Adds `torch.experimental.deterministic` flag to enforce deterministic algorithms across all of pytorch.
Adds `torch.experimental.deterministic_error_level` to allow users to choose between error/warning/silent if determinism for an operation is not available.
Adds `torch.experimental.alert_not_deterministic()` which should be called within operations that are not deterministic.
Offers both Python and ATen interfaces
Issue https://github.com/pytorch/pytorch/issues/15359
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38683
Differential Revision: D21998093
Pulled By: ezyang
fbshipit-source-id: 23aabbddd20f6199d846f97764ff24d728163737
