No user visible changes expected, these are just the internal API preparations.
Modifies the Drop API for views so that tree-views can choose to insert items
before, after and into other items.
Note: While there is support for drag-tooltips that can explain how an item
will be inserted, there is no drawing yet like in the Outliner, that indicates
if an item is inserted before, after or into. There is some work on that but
that can be done separately.
Changes:
- Removes `AbstractViewDropTarget` that was shared between tree- and
grid-views, and adds `AbstractTreeViewDropTarget` and
`AbstractGridViewDropTarget`. The tree-view needs specialized handling now,
and although they could share some code still, it's not worth having another
level of inheritance.
- Modifies the drop-target API to use `DragInfo` which contains more info about
the dragging operation than just the `wmDrag`.
- Adds `determine_drop_location()` to the `DropTargetInterface` which drop
targets can use to determine when dropping means inserting before, after or
into.
- Store the block and region in the view. This is needed unfortunately but
shouldn't be an issue since the tree view is recreated on redraws, together
with the block.
- Various smaller tweaks and additions to views as needed.
TODO (outside scope of this change): Increase row height so there is no gap
between tree view items, but keep things visually the same otherwise. This
reduces flickering while dragging.
Pull Request: https://projects.blender.org/blender/blender/pulls/109825
4525527852