Refactor notification/observation callback pattern in MutableAppContext

Pull out duplicate code and clarify some misc behavior. Some of this
existing API feels like it's probably incorrect but that needs more
thorough investigation

Co-authored-by: Mikayla <mikayla@zed.dev>
46fef69b1aForLoveOfCats committed on 8/9/2022, 11:03:25 PMparentab76049
1 file changedLine totals unavailable