Call from jit operators

[dfalbel]

This would allow calling JIT registered operators without the need to manually create wrappers in C++. For future reference:

We need to port the logic here into R: https://github.com/pytorch/pytorch/blob/47834679ba2f869e66450a74e2add4c04f0006e9/torch/csrc/jit/python/pybind_utils.h#L874-L947

Once we have it, next step should be similar to simply calling the found operation:

https://cs.github.com/pytorch/pytorch/blob/47834679ba2f869e66450a74e2add4c04f0006e9/torch/csrc/jit/python/pybind_utils.h#L1182