R1:a40c40fade6a

Drive query ordering and paging more cohesively

Summary:
Ref T7803. Ordering and paging are inherently intertwined, but they often aren't driven by the same data right now.

Start driving them through the same data:

- `getOrderableColumns()` defines orderable and pageable columns.
- `getPagingValueMap()` reads values from a cursor.

This is generally sufficient to implement both paging and ordering.

Also, add some more sanity checks to try to curtail the number of ambiguous/invalid orderings…