[LTC] Upstream LazyTensor <=> at::Tensor utils (#70066)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70066
This commit upstreams utils to convert at::Tensors into LazyTensors and
vice versa.
Test Plan:
Covered by test_ptltc on the lazy_tensor_staging branch since TorchScript
Backend hasn't merged yet.
Reviewed By: desertfire
Differential Revision: D33171590
Pulled By: alanwaketan
fbshipit-source-id: b297ff5fc8ca1a02d30e16ad2249985310e836a9
