R1:256fcf37211e

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…