[Idea/v9] Emit scrolling-related events

[Daofeng Wu]

Discussed in #364

^{Originally posted by IljaDaderko April 2, 2021}
I'm writing some logic that needs to be started on scroll start and ended when scrolling ends / becomes idle.

I can detect scroll start with scrolbar.addListener listener, but I can't seem to find anything that indicates "stop" event i.e. when scrollbars become idle and user is no longer pressing on the screen / using mouse wheel.

Is event like this exposed? If not what would be right approach here?