Make formatOrderClause() safer

Summary:
Ref T7803. Instead of trusting subqueries to provide safe values, escape them explicitly.

(We'll probably have a few cases somewhere where this doesn't work, but can make them the exception rather than the rule.)

Test Plan: Issued all "order" queries in Diffusion.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7803

Differential Revision: https://secure.phabricator.com/D12351