Added possibility to index scalars by bool masks (#21030)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21030
ghimport-source-id: 7a66ca096c62d050a38a6fcc9f6b2d61e387eb34
Differential Revision: D15530498
Pulled By: izdeby
fbshipit-source-id: d5d38f9610caa55fb7179d41f568c5ea5fa1f2e2
