RFR: Pinning humongous regions should be allowed

[Aleksey Shipilev]

This is the regression from region FSM refactoring: we should allow pinning humongous regions. The
good thing is that we do not have to mark humongous regions as "Pinned" or do critical_pins ops,
because they are not moving. Humongous objects acquired via GetPrimitiveArrayCritical are referenced
via JNI handles, so pinning info is also not needed to avoid their reclamation.

Fix:
  http://cr.openjdk.java.net/~shade/shenandoah/region-humongous-pin/webrev.01/

Testing: hotspot_gc_shenandoah (also new test that used to fail)

Thanks,
-Aleksey