Improve drag-and-drop reliability at the bottom of the Scene tree dock

[Torguen]

Godot version:

3.2.4 rc2 mono

OS/device including version:

win10 64

Issue description:

A kinematic node cannot be positioned below a sprite, however the opposite can happen.

Steps to reproduce:
Create a scene
Add a kinematic node and a sprite being children of another node.
Try positioning one below the other and vice versa.

Minimal reproduction project:

[Calinou]

This is not an issue with the node types in themselves. It's just that drag-and-drop at the bottom of the scene tree is finnicky. It's not impossible to reorder the nodes the way you want using drag-and-drop, but it's difficult.

As a workaround, you can reorder nodes by pressing Ctrl + Up arrow and Ctrl + Down arrow after selecting a node in the Scene tree dock.

[Torguen]

and why is it so easy with the sprite node?

[Calinou]

and why is it so easy with the sprite node?

Maybe because it contains child nodes?

[Torguen]

Well I have no idea, I don't know why that would matter (the fact that it has child nodes).

[nmrkr]

This appears to be a visual problem, not a functional one. The drop indicator line appears above the item instead of below, but the drop still works as expected. Seems to happen only happen on nodes with children and only on the upper half of the drop zone. This makes it very noticeable on the last node because there is now lower half. If you watch closely, you can see the drop indicator appear above the last item in @Torguen's GIF, but for clarity I recorded an extended version.

[kleonc]

Fixed by #52095/#52096.

[Calinou]

Closing per @kleonc's comment.