data event from style mutations should be fired synchronously

[jfirebaugh]

Currently, if you mutate the style via setPaintProperty or some other runtime styling API, the corresponding data event (with dataType property equal to style) is not fired until the subsequent repaint, which is asynchronous. I think this event should be fired immediately instead:

• The change is observable with respect to getPaintProperty or comparable accessor immediately, and it seems like the event should fire as soon as the change becomes observable.
• It's necessary for Refactor to simplify Map #2741: Map will use the data event as the consistent trigger for a new frame, rather than wrapping each Style method and calling _update(true) manually.
• The current behavior is causing each style mutation to trigger two repaints: one from the manual _update(true), and a second one from the data event that's triggered during the first repaint.

[jfirebaugh]

Another reason: if the data event is triggered from within style.update(), as it is now, calling map.remove() in response to that event causes a crash.