R1:d4847c3eeb78

Convert simple query subclasses to use internal cursors

Summary:
Depends on D20291. Ref T13259. Move all the simple cases (where paging depends only on the partial object and does not depend on keys) to a simple wrapper.

This leaves a smaller set of more complex cases where we care about external data or which keys were requested that I'll convert in followups.

Test Plan: Poked at things, but a lot of stuff is still broken until everything is converted.

Reviewers: amckinley

Reviewed By: amckinley…