Implement tensor.refine_names (#25842)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25842
`tensor.refine_names(*names)` takes `tensor` and attempts to name its
dimensions `names` out-of-place. If a dimension `i` already had a name,
then it cannot be changed (so tensor.names[i] must equal names[i]);
if the original dimension did not have a name, then the new name
(names[i]) can be anything.
`tensor.refine_names(*names)` also accepts a glob '*' that greedily selects
names from `tensor`. Here are some examples:
- `Tensor[None].refine_names('N') -> Tensor[N]`
- `Tensor[N].refine_names('N') -> Tensor[N]`
- `Tensor[N].refine_names('D') -> Error!`
- `Tensor[N].refine_names(None) -> Error!`
- `Tensor[None, None].refine_names('*', D) -> Tensor[None, D]`
Test Plan: - new tests [namedtensor ci]
Differential Revision: D17255548
Pulled By: zou3519
fbshipit-source-id: fdbdb3a12f24fbe37ce1e53ed09dc8a42589d928
