Julian Eisel
4ee2d9df42
Adds an easy way to add drop support for tree-view rows. Most of the work is handled by the tree-view UI code. The tree items can simply override a few functions (`can_drop()`, `on_drop()`, `drop_tooltip()`) to implement their custom drop behavior. While dragging over a tree-view item that can be dropped into/onto, the item can show a custom and dynamic tooltip explaining what's gonna happen on drop. This isn't used yet, but will soon be for asset catalogs. See documentation here: https://wiki.blender.org/wiki/Source/Interface/Views#Further_Customizations