RFR: Backport reshaped write barrier expansion to JDK11

[Roman Kennke]

Hi Roland,

>> http://cr.openjdk.java.net/~rkennke/shjdk11-wb-expansion/webrev.00/
> 
> Code you remove from ifnode.cpp is now done in
> ShenandoahBarrierSetC2::ideal_node():

Ok right. I reverted those parts, which only leaves a few
evacuation_in_progress_test() -> heap_stable_test() renamings necessary:

http://cr.openjdk.java.net/~rkennke/shjdk11-wb-expansion/webrev.01/

Is that correct now?

Roman