Merge type stubs torch nn parallel (#102194)
Fixes merge issue for #101528
In the above PR, `torch.nn.parallel.parallel_apply.get_a_var` was marked private to appease the [public interface linter](https://github.com/pytorch/pytorch/actions/runs/4999216467/jobs/8955582204#step:14:21666): https://github.com/pytorch/pytorch/pull/101528/commits/ceeb242bc7a8291c2f108659e46fd81d418380ec
This broke CI pipelines running external dependencies that expected `get_a_var`'s name to not change. In this PR, we change the name back to `get_a_var` and include it in the `__all__` instead.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102194
Approved by: https://github.com/ezyang
