Bug 263413 [DataBinding] Widget<Value|List>Property and Viewer<Value|Set|List>Property should be public
The base Widget*Property and Viewer*Property perform some standard stuff like defaulting the realm to the display realm of the widget, and wrapping the observable in an ISWTObservable or IViewerObservable decorator. In addition, WidgetValueProperty implements listeners using SWT's untyped listener API. We should make these classes public so that downstream projects like Nebula can consume them.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/internal/databinding/viewers/CheckboxViewerCheckedElementsProperty.java
ViewerSetProperty {
	private final Object elementType;
	/**
	 * @param elementType
	 */
	public CheckboxViewerCheckedElementsProperty(Object elementType) {
		this.elementType = elementType;
	}
	public Object getElementType() {
		return elementType;
	}
	protected final Set createElementSet(StructuredViewer viewer) {
		return ViewerElementSet.withComparer(viewer.getComparer());
	}
	public INativePropertyListener adaptListener(
			ISimplePropertyListener listener) {
		return new CheckStateListener(listener);
	}
	public void doAddListener(Object source, INativePropertyListener listener) {
		((ICheckable) source)
				.addCheckStateListener((ICheckStateListener) listener);
	}
	public void doRemoveListener(Object source, INativePropertyListener listener) {
		((ICheckable) source)
				.removeCheckStateListener((ICheckStateListener) listener);
	}
	private class CheckStateListener implements INativePropertyListener,