void clear() {
		modificationNumber++;
		EdgeSet es = parentGraph.edges();
		if (es.size() > 0) {
			es.clear();
		}
		if (size() > 0) {
			nextIndex = 0;
			keyIndices.removeAll();
			for (int i = 0; i < capacity; i++) {
				firstOutgoingEdge[i] = null;
				firstIncomingEdge[i] = null;
				lastOutgoingEdge[i] = null;
				lastIncomingEdge[i] = null;
				vertices[i] = null;
			}
		}
	}
Remove all of the vertices from this VertexSet without changing
the capacity. Much faster than removing each vertex individually.
The EdgeSet for this graph gets cleared first.
Ghidra/Framework/Generic/src/main/java/ghidra/util/graph/VertexSet.java