[LT] Add a new backend interface [DUP of the original] (#81662)
This is a dup of https://github.com/pytorch/pytorch/pull/76517 which is failing because Jiewen needs to resign the CLA.
Summary:
This commit introduces a new set of BackendImplInterface: GetDefaultDeviceOrdinal
and SetDefaultDeviceOrdinal. It allows backend to specify their own default
device, e.g, 1 for XLA and 0 for CUDA/CPU.
Test Plan:
./build/bin/test_lazy --gtest_filter=BackendDeviceTest.*
ghstack-source-id: b4adfef49253e51bffbbf40d356188a92c98994d
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76517
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81662
Approved by: https://github.com/JackCaoG, https://github.com/wconstab
