* Refactor: use pointer down state for alt duplication flag
* Refactor: use pointer down state for drag state
* Refactor: simplify over scrollbars check
* Refactor: move pointer move handler out of pointer down handler
* Refactor: move pointer up handler out of pointer down handler
* Refactor: further simplify scrollbar check state in pointer down event
* Refactor: pull out initial pointer down state creation