R1:a43473c4b65c

Begin formalizing query orders

Summary:
Ref T7803. Queries currently have a single `getPagingColumn()`, which is oversimplified and insufficient to describe many ordering operations. Frequently, orders must span multiple columns.

Move toward an "order vector", which is a list of orderable values like "name, id". These map directly to columns, and are sufficient to actually describe orders. The more modern Query classes (Maniphest, Repository) essentially do this manually anyway.

Test Plan:
- Added and…