R1:7d41535010aa

When a task card is edited, emit update events for old boards and parent boards

Summary:
Ref T4900. When a card is edited, we currently emit an update notification for all the projects the task is tagged with. This isn't quite the right set:

- We want to emit notifications for projects the task //was previously// tagged with, so it can be removed from boards it should no longer be part of.
- We want to emit notifications for ancestors of projects the task is or was tagged with, so parent project…