Use some more human-readable Conduit keys in updated API methods

Summary:
Ref T12074. This uses more consistent Conduit keys for constraint names.

This is a minor compatibility break on watchers/members but since these methods are more useful now this is probably a good time to try to get away with it, and a more consistent API is better in the long run. I need to issue compatibility guidance for the milestones thing anyway and that one isn't avoidable, so try to rip the bandage off all in one go.

Test Plan: Reviewed new constraint names from console, called methods using them.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12074

Differential Revision: https://secure.phabricator.com/D17161