Change TensorMeta to use tensor subclass.
This means it can be fed through traditional PyTorch C++ code
(although currently it does not work, as the __torch_dispatch__
implementation is stubbed to always throw an error.)
Signed-off-by: Edward Z. Yang <ezyangfb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76759
Approved by: https://github.com/mruberry
