Add kl divergence between normal and laplace distribution. (#68807)
Summary:
Fixes [https://github.com/pytorch/pytorch/issues/68746]
![KL_normal_laplace](https://user-images.githubusercontent.com/35850237/143008244-f304cee1-9583-4de1-b0d0-5751ebdb8188.png)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68807
Reviewed By: H-Huang
Differential Revision: D32750391
Pulled By: neerajprad
fbshipit-source-id: 129e6ef60d6e244d0d6b02b3944bfd5d8b06edcb