add serialization of interface (#25227)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25227
Adds cases to NamedType serialization to so that interfaces are written.
Similar implementation to NamedTuples
Test Plan: Imported from OSS
Differential Revision: D17066674
Pulled By: zdevito
fbshipit-source-id: fda5419260fad29e8c4ddb92de1d3447d621d982
