private Set<AttributedVertex> getAllDownstreamVerticesFromSelected() {
		Set<AttributedVertex> downstream = new HashSet<>();
		Set<AttributedVertex> targets = getUnselectedTargetVerticesFromSelected();
		while (!targets.isEmpty()) {
			downstream.addAll(targets);
			growSelection(targets);
			targets = getUnselectedTargetVerticesFromSelected();
		}
		return downstream;
	}
Ungroup the selected vertices. If the focusedVertex is no longer in the graph, null it. This
will happen if the focusedVertex was the GroupVertex
Ghidra/Features/GraphServices/src/main/java/ghidra/graph/visualization/DefaultGraphDisplay.java