RFR: 8235355: Shenandoah: Resolve deadlock between OOM handler and nmethod lock

[Roman Kennke]

JDK-8235337 changed OOM scoping, but unfortunately it causes a deadlock.
See bug report for more details:

https://bugs.openjdk.java.net/browse/JDK-8235355

The proposed fix ensures that we're entering the nmethod lock and OOM
scope in the right and the same order always. It reverts JDK-8235337 and
puts an extra OOM scope on the path that caused the original bug.

http://cr.openjdk.java.net/~rkennke/JDK-8235355/webrev.00/

Testing: hotspot_gc_shenandoah, specjvm with +aggressive and
+ShenandoahOOMDuringEvacALot

Can I please get a review?

Thanks,
Roman