Issue Description:

This doesn't work:

        av.addObserver(
            self, forKeyPath: #keyPath(AVPlayerViewController.isReadyForDisplay), options: .new, context: nil)

The problem is that we are trying to KVO observe changes in an AVPlayerViewController's "isReadyForDisplay" property. But no change notifications are triggered. Why? The reason is that "isReadyForDisplay", although it is now officially the Swift name of this property, is actually only the getter name; the setter name is "readyForDisplay", and that's what we are trying to observe, i.e. setting.

So I'm suggesting that the new renamification which uses the getter with "is" as the name of the property in Swift is going to mislead users and their KVO attempts will fail. But maybe #keyPath could be smarter about this and translate behind the scenes into the real name of the property?