R1:411456084448

Modernize more paging/order queries

Summary:
Ref T7803. Removes some getReversePaging().

This also fixes `null` column handling, by adding an explicit `'null'` key with possible values "head" (put NULL before other values) or "tail" (put NULL after other values).

Maniphest has some glitchiness in paging through NULLs right now, but I believe it's all pre-existing and will be resolved when it fully converts. Diffusion is fully converted and pages through NULL correctly.

Test Plan:
- Failed to identify…