Change Draggable behavior to pick up the instance with the highest layer and Z order

[Tristan Rhodes]

Description

If a player tries to drag overlapping objects, it drags the first created object.
This doesn't make sense to the players, they expect the dragging to work like the real world, where the top-most object gets dragged first.

In this example, I created 52 objects with events and changed their animations.

GDevelop_tFyjyt2571.mp4

Solution suggested

Change the "Draggable" behavior to first pick the object with the highest z order and layer.

[Tristan Rhodes]

I wonder if these objects created by events all have the same z order (I will debug tomorrow)