Summary:
Fixes T7563. Fixes T5201. Reframe this as two separate operations:
- Move before or after a task.
- Move to the beginning or end of a priority.
Then:
- Make all the order queries unambiguous and properly reversible, with an explicit `id` order.
- Just reuse `ManiphestTask` to get results in the correct order.
- Simplify the actual transaction apply logic.
- Detect and recover from cases where tasks have identical or similar subpriorities.
Test Plan:
- Wrote and executed unit tests.
- Dragged and dropped tasks within priorities and between priorities in the main Maniphest view.
- Dragged and dropped tasks within priorities in the workboard view, when ordered by priority.
- Also poked at the "natural" order, but that shouldn't be affected.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: chad, epriestley
Maniphest Tasks: T5201, T7563
Differential Revision: https://secure.phabricator.com/D12121
