codegen: Allow string arguments to have defaults (#45665)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45665
Fixes #43944
Note that the codegen doesn't use a proper parser so, in the same way as with lists, the string `, ` cannot appear in defaults or it will be interpreted as a splitting point between arguments.
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D24141835
Pulled By: ezyang
fbshipit-source-id: 578127861fd2504917f4486c44100491a2c40343
