Fix packages(project) to work properly and add it to "MailableFunctionDatasource"
This blames back to D14013, where it looks like packages(..) was added mostly as a general nice-to-have as part of a larger modernization change.
Test Plan: Ran a packages(project) query in Differential, got accurate results (previously: no results).
Reviewed By: amckinley
Maniphest Tasks: T13210
Differential Revision: https://secure.phabricator.com/D19747