[CustomOp] Add Dispatcher error callback (#101015)
The PyTorch Dispatcher's "no kernel found for DispatchKey" error message
is a bit long and winded. This PR adds a way to add a custom error
callback and changes the CustomOp API to use the custom error callback
to deliver better error messages.
Test Plan:
- new tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101015
Approved by: https://github.com/ezyang
