QGuiApplication::devicePixelRatio() provides out-of-date value if displays change after app launch

QGuiApplication::devicePixelRatio() caches its value to improve performance. However, its cache is not refreshed when the system's displays change (if a HiDPI/Retina display is added or removed, or if a display's devicePixelRatio changes), so it can provide an out-of-date value.