Add CUDA support to a user-created torch.futures.Future (#56517)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56517
Currently a torch.futures.Future could wrap a CUDAFuture, but it could not create one from scratch. This prevented users from using CUDAFutures in some occasions, for example when using `rpc.functions.async_execution`, or in their own code. I don't see any reason for such a limitation, hence here I add support for this.
ghstack-source-id: 127261554
Test Plan: Added a test later in the stack
Reviewed By: mrshenli
Differential Revision: D27887190
fbshipit-source-id: ecbb39c1ad7cd189d478ded9c361448f05a270ad
