RFR: Add JFR parallel and concurrent events

[Roman Kennke]

Looks ok to me.
Thanks!

Roman


> The patch adds JFR parallel and concurrent events for Shenandoah.
> 
> It also reshuffles a few includes and moves
> ShenandoahWorkerTimingsTracker and ShenandoahTerminationTracker to
> separate files, to avoid recursive inclusion.
> 
> 
> Webrev:
> http://cr.openjdk.java.net/~zgu/shenandoah/jfr_conc_par_events/webrev.00/index.html
> 
> 
> Test:
> 
>   tier3_gc_shenandoah (fastdebug and release)
> 
> Thanks,
> 
> -Zhengyu
> 
>