add str builtin support (#20188)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20188
ghimport-source-id: 390b889f67155eb6168a96d05307ec4e86f5c631
Differential Revision: D15228812
Pulled By: zdevito
fbshipit-source-id: 789efa2e0b2f9518ed97ac877b59637e5b0ebcf4
