Make it easier to construct multi-column paging clauses from Query classes
Summary:
We currently have two giant messes for paging across multiple columns (usually because one column is not unique), and I'm about to add a third for Maniphest.
Provide a more structured way to build these A > a OR (A = a AND B > b) clauses.
Test Plan: Set page size to 2 for Differential and Diffusion and paged forward and backward with a bunch of different orders set. Pages worked as expected.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2625
Differential Revision: https://secure.phabricator.com/D6971