[custom_op] Make repeated registrations error gracefully (#100979)
Previously the error message went through torch.library. This PR changes
it so that on each custom_op.impl_* call:
- we store a (function, location) tuple
- if a (function, location) tuple exists already, then we raise an
error.
This logic already existed for the abstract impl (the impl for meta and
fake tensors), so this PR just extends it to the others.
Test Plan:
- new test
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100979
Approved by: https://github.com/bdhirsh, https://github.com/soulitzer
