Use authoritative PHIDs for Herald "Task Projects" condition

Summary:
Fixes T5707. After work on T5245, the $task object may not have the correct set of task PHIDs attached to it when Herald is invoked.

Instead, just fetch the authoritative set. This is simple, and Herald is not super performance sensitive (happens on a write) so hitting the DB once is fine.

Test Plan: Created a task with projects, verified the projects field contained the correct values when processed by Herald.

Reviewers: chad, btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5707

Differential Revision: https://secure.phabricator.com/D10060