Change '*' to '...' and `...` for named tensor API functions. (#26350)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26350
Python 3 lets us use `...` to perform indexing. Semantically, `...`
means "the rest of the unspecified dimensions". For example, while
indexing, one can do (for 5D `tensor`) `tensor[0, 0, ..., 0]` and
the `...` is expanded into `tensor[0, 0, :, :, 0]`.
Previously, we were using '*' to represent a similar behavior in names.
For example, `tensor.refine_names` supports things like the following:
```
x = torch.randn(2, 3, 4, 5, 6)
x_out = x.refine_names('*', 'H', 'W') # refine only the last two
dimensions
```
This PR changes it so that named tensor API functions recognize `'...'`
(in Python 2 and Python 3) and `...` (in Python 3 exclusively) instead
of `'*'`.
Test Plan: - [namedtensor ci]
Differential Revision: D17424666
Pulled By: zou3519
fbshipit-source-id: 003182879fd38ced3fea051217572a457cdaf7cf
