Add at::scalar_tensor factory function, use it instead of Type.scalar… (#15074)
Summary:
…_tensor.
This is part of a long series of paring down the Type interface.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15074
Differential Revision: D13421482
Pulled By: gchanan
fbshipit-source-id: 84010ee71fef2cb74d32d5de7858d8ed9f36b885
