Make JIT attributes t_ and ts_ store Variable instead of Tensor (#16596)
Summary:
Discussed with zdevito and we want to use Variable (with `set_requires_grad(false)`) instead of Tensor in all parts of JIT, to eliminate the distinction and the conceptual overhead when trying to figure out which one to use.
This also helps with the Variable/Tensor merge work tracked at https://github.com/pytorch/pytorch/issues/13638, which will make common functions (such as `numel()` / `sizes()` / `dim()`) on Variable much faster when finished.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16596
Differential Revision: D13979971
Pulled By: yf225
fbshipit-source-id: c69119deec5bce0c22809081115f1012fdbb7d5a
