Deprecate torch.cross default behaviour (#108760)
Long overdue this one. We may be able to change it in a few years :hopeful:.
**BC-breaking note**
This PR deprecates `torch.cross`'s default dim in favor of
`torch.linalg.cross`.
A upgrade guide is added to the documentation for `torch.cross`.
Note this PR DOES NOT remove `torch.cross`.
Fixes https://github.com/pytorch/pytorch/issues/108664
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108760
Approved by: https://github.com/albanD
