Update linalg.*norm
This PR does a number of things:
- Move linalg.vector_norm to structured kernels and simplify the logic
- Fixes a number of prexisting issues with the dtype kwarg of these ops
- Heavily simplifies and corrects the logic of `linalg.matrix_norm` and `linalg.norm` to be consistent with the docs
- Before the `_out` versions of these functions were incorrect
- Their implementation is now as efficient as expected, as it avoids reimplementing these operations whenever possible.
- Deprecates `torch.frobenius_norm` and `torch.nuclear_norm`, as they were exposed in the API and they are apparently being used in mobile (??!!) even though they were not documented and their implementation was slow.
- I'd love to get rid of these functions already, but I guess we have to go through their deprecation.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76547
Approved by: https://github.com/mruberry
