Make the query compiler emit intermediate tokens

Summary:
Ref T12137. Ref T12003. Ref T2632. Ref T7860. In all these tasks, we want to examine or interact with the query after it is parsed, but before it is compiled.

Make the compiler emit an intermediate parsed representation so we can do that.

(The next change fixes Phabricator for this new API.)

Test Plan: Ran unit tests, see also next change.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12137, T12003, T7860, T2632

Differential Revision: https://secure.phabricator.com/D17669