[custom_op] Allow constructor to infer more types (#106799)
This expands the torch._custom_ops.custom_op API to be able to construct
operators that return (int, bool, float, Scalar, List[Tensor]) to make
it more in-line with our torch.library API.
NB: there needs to be updates to our custom_op autograd registration
API. For ease of review those changes will go in the next PR up but I
can squash if requested.
Test Plan:
- new tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106799
Approved by: https://github.com/soulitzer
