[RPC Framework] Support remote device format "<workername>/<device>" (#46773)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46773
Changed the constructor of RemoteModule to accept a `remote_device` arg in the following format:
"<workername>/<device>" (e.g., "trainer0/cpu", "ps0/cuda:0")
This arg merges the original `on` and `device` arg.
Original PR issue: RemoteDevice Format #46554
ghstack-source-id: 115448051
Test Plan: buck test mode/dev-nosan caffe2/test/distributed/rpc:process_group_agent -- RemoteModule
Reviewed By: pritamdamania87
Differential Revision: D24482562
fbshipit-source-id: 5acfc73772576a4b674df27625bf560b8f8e67c1
