Move exponential_() to DistributionTemplates (#37456)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37456
Fixes #37370
Test Plan: Imported from OSS
Differential Revision: D21290781
Pulled By: pbelevich
fbshipit-source-id: 2f516b5112b9ce1c9ba8967b3758decf86d65676
