Bug 317417 [Model] StackElement should be abstract and interface
StackElement is only a marker for improved containment hierarchies. We should at least make it abstract but also as an interface like WindowElement, ...
bundles/org.eclipse.e4.ui.model.workbench.edit/src/org/eclipse/e4/ui/model/application/ui/basic/provider/BasicItemProviderAdapterFactory.java
/**
	 * This keeps track of the one adapter used for all {@link org.eclipse.e4.ui.model.application.ui.basic.MWindow} instances.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	protected WindowItemProvider windowItemProvider;
	/**
	 * This creates an adapter for a {@link org.eclipse.e4.ui.model.application.ui.basic.MWindow}.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	@Override
	public Adapter createWindowAdapter() {
		if (windowItemProvider == null) {
			windowItemProvider = new WindowItemProvider(this);
		}
		return windowItemProvider;
	}
	/**
	 * This keeps track of the one adapter used for all {@link org.eclipse.e4.ui.model.application.ui.basic.MTrimmedWindow} instances.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	protected TrimmedWindowItemProvider trimmedWindowItemProvider;
	/**
	 * This creates an adapter for a {@link org.eclipse.e4.ui.model.application.ui.basic.MTrimmedWindow}.
	 * <!-- begin-user-doc -->