Scroll event should report progress to Navigator

[JayPanoz]

ScrollSnapper reports progress to Navigator in many cases (when it has to go to a progression or an id for instance), but the scroll event itself is not yet supported.

That may be unexpected for developers who keep track of progress through the positionChanged listener in paginated mode or FXL, as they would then need to implement this for scrollable mode entirely.

Of course there are implementation details to take into account (throttling, etc.) so this issue can serve as a place to discuss these and log what’s being implemented.