Fast combined C++/Python/TorchScript/Inductor tracebacks

[vanbasten23]

Thanks! This is really cool.

@zdevito

std::shared_ptr<torch::CapturedTraceback> tb0 = 
  torch::CapturedTraceback::gather(/*python=*/true, /*script=*/true, /*cpp=*/true);
  
std::shared_ptr<torch::CapturedTraceback> tb1 = 
  torch::CapturedTraceback::gather(/*python=*/true, /*script=*/true, /*cpp=*/true);

I wonder why we need to call torch::CapturedTraceback::gather twice with the same arguments.