torch.nn.functional.gumbel_softmax #27078 (#28121)
Summary:
**Comments:**
* Grad check from https://github.com/pytorch/pytorch/blob/848d1ba13a3f77bb6f14656f2d84e2228e37a8ef/test/test_nn.py#L8898 not added
* Double data type as seen in https://github.com/pytorch/pytorch/blob/848d1ba13a3f77bb6f14656f2d84e2228e37a8ef/test/test_nn.py#L8916 not tested
**Issue:**
https://github.com/pytorch/pytorch/issues/27078
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28121
Differential Revision: D18008515
Pulled By: yf225
fbshipit-source-id: 9363fe9430df0f2bfd337cc788b11ac93adaa360
