[11] RFR, 2020-04-20, Bulk backports to sh/jdk11

[Aleksey Shipilev]

https://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20200420/webrev.01/

This backports a few leftovers that passed testing recently:

 [backport] 8242229: Shenandoah: inline ShenandoahHeapRegion liveness-related methods
 [backport] 8242353: Shenandoah: micro-optimize region liveness handling
 [backport] 8242365: Shenandoah: use uint16_t instead of jushort for liveness cache
 [backport] 8225216: gc/logging/TestMetaSpaceLog.java doesn't work for Shenandoah
 [backport] 8241142: Shenandoah: should not use parallel reference processing with single GC thread
 [backport] 8242641: Shenandoah: clear live data and update TAMS optimistically

Testing: hotspot_gc_shenandoah {fastdebug, release}

-- 
Thanks,
-Aleksey