Fix out= function semantics for named tensors. (#24028)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24028
Previously, torch.abs(tensor, out=out) would ignore the names of the
`out` tensor and overwrite them with the names of `tensor`.
This patch changes the behavior to the following:
1) If `out` does not have names, then overwite them with `tensor.names`.
2) If `out` does have names, then check that `out.names` equals
`tensor.names`.
This patch also includes the following clean ups:
- renamed `default_names` to `FIXME_default_names` because it is
inefficient and needs to be fixed.
- Renamed impl::internal_get_names / impl::internal_has_names to
impl::get_names / impl::set_names. Devs should feel free to use them, so
I removed the internal_ prefix.
- Moved internal_set_names to NamedTensor.{h, cpp}. These functions
still have the internal_ prefix because their use requires caution.
Test Plan: - [namedtensor ci]
Differential Revision: D16763387
Pulled By: zou3519
fbshipit-source-id: 57dcc7c759246def0db2746d1dca8eddd5e90049
