added List as an option to the unflattened_size (#49838)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/49743
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49838
Reviewed By: mruberry
Differential Revision: D25727971
Pulled By: ngimel
fbshipit-source-id: 60142dae84ef107f0083676a2a78ce6b0472b7e1
