Refactor TupleType to take a NamedTupleSpec (#21836)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21836
ghimport-source-id: 91cab735765ff875046b42864188e86b8487b0ae
Test Plan: Imported from OSS
Reviewed By: zdevito
Differential Revision: D15860003
Pulled By: jamesr66a
fbshipit-source-id: 62a99a212ae6f9af83a90305e443f2dd05588292
