R1:891355297074

Store "resigned" as an explicit reviewer state

Summary:
Fixes T11050. Today, when a user resigns, we just delete the record of them ever being a reviewer.

However, this means you have no way to say "I don't care about this and don't want to see it on my dashboard" if you are a member of any project or package reviewers.

Instead, store "resigned" as a distinct state from "not a reviewer", and treat it a little differently in the UI:

- On the bucketing screen, discard revisions any responsible user has…