QQuickAccessibleAttached / Accessible QML: no way to specify the value for QAccessible.state().disabled in QML

This is needed to support accessibility in scenarios where we show text input fields that are disabled (cannot be interacted with).

While the QAccessible class's state() supports a "disabled" value, that value doesn't exist in the Accessible QML namespace and thus it doesn't get plumbed through QQuickAccessibleAttached and QAccessibleQuickItem