[14] RFR (S) 8243494: Shenandoah: set counters once per cycle

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8243494
  https://hg.openjdk.java.net/jdk/jdk/rev/d0e8e1d3d8e3

This is a part of bulk backport of enhanced Shenandoah logging to 14u. Again, the context is a bit
different, because phase roots list is a bit different.

14u webrev:
  https://cr.openjdk.java.net/~shade/8243494/webrev.14u.01/

Testing: hotspot_gc_shenandoah, eyeballing gc logs

-- 
Thanks,
-Aleksey