support complex types for tanh_cuda and tanh_backward_cuda (#38786)
Summary:
Builds on https://github.com/pytorch/pytorch/issues/37791
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38786
Differential Revision: D21666138
Pulled By: anjali411
fbshipit-source-id: cbd313b8fd21109aadd614c60259b9dc505771a5
