Better named tensor error messages. (#26974)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26974
Suggest `Tensor.rename` to rename tensors and/or drop names on named
tensors.
Test Plan: - [namedtensor ci]
Differential Revision: D17628950
Pulled By: zou3519
fbshipit-source-id: b701f46c46093046691eace698be8282d049d37a
