R1:26ba4e871720

Materialize parent project memberships

Summary:
Ref T10010. Subprojects have the following general membership rule: if you are a member of a subproject ("Engineering > Backend"), you are also a member of the parent project.

It would be unreasonably difficult to implement this rule directly in SQL when querying `withMemberPHIDs()`, because we'd have to do an arbitrarily large number of arbitrarily deep joins, or fetch and then requery a lot of data.

Instead, introduce "materailized members", which are…