[PyTorch] Add Tensor.is_nested (#73999)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73999
Seems to be the typical way to detect a flavor of TensorImpl.
ghstack-source-id: 151440167
Test Plan: Existing tests?
Reviewed By: ezyang
Differential Revision: D34665269
fbshipit-source-id: 5081a00928933e0c5252eeddca43bae0b026013d
(cherry picked from commit 7cf62a3f69f158a33c5108f7e96ea4c5520f0f15)
