Pull Request resolved: #44418


This commit uses TensorPipe's cuda_ipc channel to conduct
cross-process same-machine GPU-to-GPU communication. On the sender
side, `TensorPipeAgent` grabs a stream to each device used by the
message, let these streams wait for current streams, and passes
the streams to TensorPipe `CudaBuffer`. On the receiver side, it
also grabs a stream for each device used in the message, and uses
these streams to receive tensors and run user functions. After that,
these streams are then used for sending the response back to the
sender. When receiving the response, the sender will grab a new set
of streams and use them for TensorPipe's `CudaBuffer`.

If device maps are provided, `TensorPipeAgent::send` will return a
derived class of `CUDAFuture`, which is specifically tailored for
RPC Messages.

TODOs:
1. Enable sending CUDA RPC to the same process.
2. Add a custom CUDA stream pool.
3. When TensorPipe addressed the error for `cudaPointerGetAttributes()`,
remove `cuda:0` context initialization code in `backend_registry.py`.
4. When TensorPipe can detect availability of peer access, enable all
tests on platforms without peer access.

Differential Revision: [D23626207](https://our.internmc.facebook.com/intern/diff/D23626207/)

**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D23626207/)!
ghstack-source-id: 119821241