Support cdf for mixture_same_family distribution (#33408)
Summary:
The new added mixture_same_family should support cdf if the family has cdf implemented.
This is very useful for flow models where cdf of mixture of gassian/logistic is used to model flow
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33408
Differential Revision: D20191552
Pulled By: ezyang
fbshipit-source-id: 0bfd7973aa335c162919398a12ddec7425712297
