Add silu and hardsigmoid converter (#71453)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71453
As title
Test Plan: unit test
Reviewed By: frank-wei
Differential Revision: D33646384
fbshipit-source-id: d86326c93e4d6bd59c9152592721f0e6ecf7f6fb
(cherry picked from commit d886380edef3388d60d529100332f9d9564f0913)
