Fully modularize Herald field values
Summary: Ref T8726. This gets rid of all the VALUE_* constants and lets Fields provide arbitrary typeaheads without upstream/JS changes.
Test Plan: Used all tokenizers. Used "Another Herald Rule". Grepped for all removed constants.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T8726
Differential Revision: https://secure.phabricator.com/D13616