Expose alias multinomial methods to ATen (#17904)
Summary:
This PR exposes the multinomialAliasSetup and multinomialAliasDraw methods.
cc: neerajprad
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17904
Differential Revision: D14700205
Pulled By: ezyang
fbshipit-source-id: 16462fb1f1ef1d560fd586632ea356b23e966ee3
