RFR (M) 8239786: Shenandoah: print per-cycle statistics

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8239786

A brief tour:
 *) ShPhaseTimings now collects worker data and cycle data into the separate counters that are
populated once per cycle. ShControlThread is then responsible for merging and printing out that data.
 *) We still have "global" view that is printed at the end of the run, but we also have "cycle" view
that is printed after each cycle. Note that printing is outside of any pause, and so the logging is
effectively asynchronous!
 *) Where possible, "cycle" view shows the per-worker statistics.

Webrev:
  https://cr.openjdk.java.net/~shade/8239786/webrev.01/

Sample piece of GC log:
  https://cr.openjdk.java.net/~shade/8239786/gc-log-sample.txt

Testing: hotspot_gc_shenandoah, eyeballing logs; more aggressive testing is running

-- 
Thanks,
-Aleksey