[14] RFR (S) 8243478: Shenandoah: avoid implicit worker_id = 0

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8243478
  https://hg.openjdk.java.net/jdk/jdk/rev/cfc5b66e39c8

This is a part of bulk backport of enhanced Shenandoah logging to 14u. Again, the context is a bit
different, because there is no split between weak/strong roots in 14u and closures are named
differently.

14u webrev:
  https://cr.openjdk.java.net/~shade/8243478/webrev.14u.01/

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey