[LTC] Upstream utils to extract BackendDevice from at::Tensor (#70069)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70069
This commit upstreams utils to extract BackendDevice from at::Tensor.
Test Plan: ./build/bin/test_lazy --gtest_filter=BackendDeviceTest.GetBackendDevice*
Reviewed By: samdow
Differential Revision: D33293160
Pulled By: alanwaketan
fbshipit-source-id: 78647239f90b4d04adce84ae6022b8983ad30c09
