Add getStreamFromPool to DeviceGuardImplInterface (#57046)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57046
We intend to merge CUDAFuture into ivalue::Future by using DeviceGuardImplInterface to avoid explicitly referring to CUDA. For that we need to add two methods to DeviceGuardImplInterface. In this PR, we add a method to get a stream from the global ATen pool.
ghstack-source-id: 127713137
(Note: this ignores all push blocking failures!)
Test Plan: Used later in this stack
Reviewed By: ezyang
Differential Revision: D28029159
fbshipit-source-id: 5055d84c1f3c2a4d86442f3149455c5ebd976dea
