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.MInputPart} instances.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	protected InputPartItemProvider inputPartItemProvider;
	/**
	 * This creates an adapter for a {@link org.eclipse.e4.ui.model.application.ui.basic.MInputPart}.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	@Override
	public Adapter createInputPartAdapter() {
		if (inputPartItemProvider == null) {
			inputPartItemProvider = new InputPartItemProvider(this);
		}
		return inputPartItemProvider;
	}
	/**
	 * This keeps track of the one adapter used for all {@link org.eclipse.e4.ui.model.application.ui.basic.MPartStack} instances.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	protected PartStackItemProvider partStackItemProvider;
	/**
	 * This creates an adapter for a {@link org.eclipse.e4.ui.model.application.ui.basic.MPartStack}.
	 * <!-- begin-user-doc -->