[SR] Sigmoid out variant calls fast_sigmoid (#75661)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75661
`fast_sigmoid` is a variant of sigmoid in NNC that is implemented in terms of `fast_tanh` (which is a fast rational function approximation).
ghstack-source-id: 155604086
Reviewed By: navahgar, hlu1
Differential Revision: D35481390
fbshipit-source-id: 1d64b5c375539f3b2461a1f3d9b86cd696eae7a1
(cherry picked from commit 8106c2512b8d7b373cb6545a43c3e8fc04805c4b)
