Add thread-local-state NamesMode and NoNamesGuard (#24367)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24367
NamesMode determines whether or not to ignore the names field of
TensorImpl. In particular, when it is disabled, all tensors are treated
as unnamed.
Test Plan: - New tests [namedtensor ci]
Differential Revision: D16915806
Pulled By: zou3519
fbshipit-source-id: 21f7ff1eadebd678d6cd9a16ff25dd6134272b76
