Add interfaces in lr_scheduler.pyi (#23934)
Summary:
Some interfaces of schedulers defined in lr_scheduler.py are missing in lr_scheduler.pyi.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23934
Differential Revision: D16726622
Pulled By: ezyang
fbshipit-source-id: 45fd2d28fbb658c71f6fcd33b8997d6ee8e2b17d
