Move version_counter_ to TensorImpl (#18223)
Summary:
According to https://github.com/pytorch/pytorch/issues/13638#issuecomment-468055428, after the Variable/Tensor merge, we may capture variables without autograd metadata inside an autograd function, and we need a working version counter in these cases. This PR makes it possible by moving `version_counter_` out of autograd metadata and into TensorImpl, so that variables without autograd metadata still have version counters.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18223
Differential Revision: D14735123
Pulled By: yf225
fbshipit-source-id: 15f690311393ffd5a53522a226da82f5abb6c65b
