R1:e869e7df0b79

When logged-out users hit a "Login Required" dialog, try to choose a better "next" URI

Summary:
Ref T10004. After a user logs in, we send them to the "next" URI cookie if there is one, but currently don't always do a very good job of selecting a "next" URI, especially if they tried to do something with a dialog before being asked to log in.

In particular, if a logged-out user clicks an action like "Edit Blocking Tasks" on a Maniphest task, the default behavior is to send them to the standalone page for…