[Godot] Skeleton rendering separation

[misaki-eymard]

A SpineSlotNode can be used to insert another object between the draw order of a skeleton's slots, but this is not well suited for temporarily inserting objects that were originally moved separately, e.g. two characters normally move separately, and one character is temporarily placed between the other's drawing order for a hug animation. If you try to do this with SpineSlotNode, you have to duplicate the character (one for when they move separately and one for when they move between certain SpineSpriteNodes) because the inserted object must be a child of SpineSpriteNode. It would be convenient if you can temporarily separate the draw order of a skeleton at the front and back, without duplicating the character, and allow another character to be sandwiched in between like the SkeletonRenderSeparator component of the spine-unity runtime.

Related forum thread:
https://esotericsoftware.com/forum/d/27253-godot-43-slot-draw-order-manipulation-at-runtime