Add contiguous_strides as a correct replacement of defaultStride (#67789)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67789
`at::defaultStride` was added in https://github.com/pytorch/pytorch/pull/18779.
As it was noted in that PR, it differs from the actual computation of
the default strides when one or more of the dimensions of the tensor are
zero. See https://github.com/pytorch/pytorch/pull/18779#discussion_r272296140
We add two functions, `contiguous_strides` and `contiguous_strides_vec`
which correct this issue and we replace the previous (wrong) uses of
`defaultStride`.
cc jianyuh nikitaved pearu mruberry walterddr IvanYashchuk xwang233 Lezcano
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D32684852
Pulled By: mruberry
fbshipit-source-id: 62997a5a97a4241a12e73e2be2e192b80b491cb1
