[Feature] Provide dragStart & dragEnd events for the legend items

[abdurrahmanyildirim]

What problem does this feature solve?

I can drag/drop rendered series.

i wanna drag series to other places from rendered echart dom.

Need support for events for dragStart, dragEnd

What does the proposed API look like?

Not sure about api. draggable option can be added to activate events.

[flibbles]

I'd second a a feature like this. I'm currently creating an adaption for ECharts with TiddlyWiki, and it's going to feel incomplete if users cannot move graph nodes around and get an event specifying the new location.