RFR: Full GC should compact humongous regions

[Roman Kennke]

> http://cr.openjdk.java.net/~shade/shenandoah/humongous-moves/webrev.01/
> 
> This implements humongous regions moves during last-ditch Full GC. This allows Shenandoah to survive
> humongous-fragmenting workloads, at the expense of potentially longer Full GC, when the alternative
> is OOME. This mirrors the upstream G1 RFE [1]. New jtreg test is the example of such the workload,
> and it OOMEs Shenandoah in seconds without this fix.
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release}, new failing test
> 
> Thanks,
> -Aleksey
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8191565
> 

Looks good to me.