[quant][graphmode] tanh pattern and test (#36880)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/36880
Test Plan: Imported from OSS
Differential Revision: D21110105
Pulled By: z-a-f
fbshipit-source-id: 45b33ec203c333c1b40376bcf768f2a0eaa8cc5e
