add support for parsing class defs to the string frontend (#17628)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17628
This is not hooked up anywhere yet, just adding support.
This shares the same restrictions as the python frontend—namely, that the only exprs allowed right now are method defs.
Reviewed By: shannonzhu
Differential Revision: D14291654
fbshipit-source-id: 7798e5ff412a52ef8803c7bae8f439e50968a73a
