[8] RFR: 2020-05-18, Bulk backports to sh/jdk8

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20200518/webrev.01/

This mostly backports the new logging to sh/jdk8:
  [backport] 8243494: Shenandoah: set counters once per cycle
  [backport] 8225216: gc/logging/TestMetaSpaceLog.java doesn't work for Shenandoah
  [backport] 8239786: Shenandoah: print per-cycle statistics
  [backport] 8243848: Shenandoah: Windows build fails after JDK-8239786
  [backport] 8243573: Shenandoah: rename GCParPhases and related code
  [backport] 8244180: Shenandoah: carry Phase to ShWorkerTimingsTracker explicitly
  [backport] 8244226: Shenandoah: per-cycle statistics contain worker data from previous cycles
  [backport] 8244326: Shenandoah: global statistics should not accept bogus samples

It took significant time to adjust the patches for 8u, so please review carefully.

Testing: hotspot_gc_shenandoah {fastdebug,release}, eyeballing the gc logs

-- 
Thanks,
-Aleksey