add on_scroll_end event

[Lendemor]

From experimentation, on_scroll is kinda spammy during scroll events, so it might be useful to have one that fire once per scroll, when it end.

It's a no_args_event_spec for now because I didn't find much useful data inside the event that is fired on that trigger.

[codspeed-hq]

CodSpeed Performance Report

Merging #5401 will not alter performance

_{Comparing lendemor/add_scroll_end_event (1862a81) with main (85af94b)}

Summary

✅ 8 untouched benchmarks

[adhami3310]

safari doesn't support this, do we care?

[Lendemor]

safari doesn't support this, do we care?

That's a Safari problem isn't it?
We follow the MDN specifications, if Safari doesn't want to support it, not much we can do, but no reason to keep other browsers from using the feature.

[masenf]

tentative approval provided docs are appropriately updated