Propagate "unexpandable" PHIDs to feed notification recipient expansion

Summary:
See PHI466. Ref T13108. Somewhat recently, new rules were added so that "Resigning" from a revision takes you off the default recipient list, even if you're still a member of a project or package that is still a reviewer or subscriber.

However, these rules don't currently apply to the similar expansion which occurs in notifications. If you resign from a revision you may still get some notifications (just not email) if a package or project you're a member of is a reviewer or subscriber.

(Possibly these should eventually share more code, but just get things working for now.)

Test Plan:

• Created a revision as A.
• Added B as a reviewer.
• Added a package B is an owner for as a reviewer.
• As B, resigned. (Make sure B is also not an explicit subscriber.)
• Commented on the revision as A.
  • Before: B is included in the expanded notification recipient list.
  • After: B is no longer included in the expanded notification recipient list.

Maniphest Tasks: T13108

Differential Revision: https://secure.phabricator.com/D19244