Implement tensor.align_as(other), change tensor.align_to(names) (#25843)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25843
`tensor.align_to(*names)` permutes the dimensions of `tensor` and adds
additional 1-sized dimensions such that the output tensor has dimensions
in the same order as `names`. All dimensions of `tensor` must be
present in `names`, in addition, this function requires that all dims of
`tensor` be named.
`tensor.align_as(other)` is equivalent to
`tensor.align_to(*other.names)`.
I'm planning on changing `torch.align_tensors(*tensors)` to align closer
to these semantics because there didn't seem to be a clear use case for the old
semantics that preserve unnamed dimensions. That will come in a future
change.
Test Plan: - new tests [namedtensor ci]
Differential Revision: D17255549
Pulled By: zou3519
fbshipit-source-id: 1e437ad81e9359b4d5bd0e7e64c3a1be441fc3e3
