public DropTarget getPrimaryDropTarget() {
		return primaryDropTarget;
	}
Combines two drop targets and sends events to them in priority order.  If the first drop target
accepts the event, then the second drop target is not accessed. 
<p>
Either of the given drop targets can be an instance of CascadedDropTarget, effectively creating 
a tree structure of drop targets.
Ghidra/Framework/Generic/src/main/java/ghidra/util/CascadedDropTarget.java