feature: events for autoscroll ext

[spencercap]

awesome library! thanks for all the thoughtful work!
i doubt i'll have have time to implement this myself so am just leaving a note here in case anyone else wants to pick it up.

would be rad to have a few events for the autoscroll extensions such as:

• autoscroll:paused - such as on hover
• autoscroll:play - event triggered BEFORE slides move
• autoscroll:played - triggered AFTER slides start moving
• autoscroll:playing - continuous events while slides are auto scrolling/moving (+ details such as offset, active slide index, etc)

(not be confused with the autoplay events...)

i noticed that the intersection extension has some events (https://github.com/Splidejs/splide-extension-intersection/blob/36cd6359e27b3edbac3d778d53f2fbc3c07e607b/src/js/constants/events.ts#L2). i imagine the autoscroll extension could implement it similarly.