qml: hide hover areas if fading edge is not enabled in `FadingEdgeForListView.qml`

I realized this because on Qt 6.8 (unlike 6.2) the hover handlers causes the delegate instance underneath hovered to be not set. I consider that a Qt bug and don't plan to fix it at the moment, because everything else still works (tapping, dragging). If we want to fix that, we probably need to use HoverHandler in the delegate Control, instead of relying on hovered and hoverEnabled, but HoverHandler comes with its own intricacies.

I don't have strong opinion on using HoverHandler in Control instead of relying hoverEnabled/hovered, since we are already using other type of handlers. Qt has had plans of using handlers instead of Control's own handling, perhaps by getting rid of all Control's own event handling (hoverEnabled, wheelEnabled, clicked(), ...). Maybe we do that when they start doing that, as then we must have explicit HoverHandler.

Request review @chub.