Feature Request: Ability to detect scroll events

[lbeus]

I'm integrating native player which is supposed to be used to play audio resources which are distributed as part of EPUB document and referenced in reading order documents. Player preview is supposed to hide/show as you scroll vertically up/down through XHTML document.

Suggestion is to add scroll callback method to VisualNavigatorDelegate as implemented in PR
func navigator(_ navigator: any VisualNavigator, didScrollIn direction: ScrollDirection)

One more use case where this event could be used is when integrating app analytics with the reader.