Allow a higher-precision step type for Vec256::arange (#34555)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34555
This is sometimes necessary, such as when T=int and the step size is of
type double.
Test Plan: Imported from OSS
Differential Revision: D20687063
Pulled By: ezyang
fbshipit-source-id: 33086d4252d06e7539733a9b1b3d6774e177b6da
