void add(ComponentPlaceholder placeholder) {
		windowPlaceholders.add(placeholder);
		placeholder.setNode(this);
		if (placeholder.isActive()) {
			top = placeholder;
			invalidate();
		}
		WindowNode topLevelNode = getTopLevelNode();
		topLevelNode.componentAdded(placeholder);
	}
Adds a component to this node.
@param placeholder the component placeholder containing the component to be added.
Ghidra/Framework/Docking/src/main/java/docking/ComponentNode.java