add tanh + quantize unit test (#44076)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44076
add fakelowp test for tanh + quantize
Test Plan: net runner
Reviewed By: venkatacrc
Differential Revision: D23339662
fbshipit-source-id: 96c2cea12b41bf3df24aa46e601e053dca8e9481
