Compilation of promise resolution and message sending not optimal

[smarr]

Currently, PromiseMessage.resolve() and EventualMessage.getTarget() cannot be inlined, because they are not devirtualized.
Might give a bit of performance improvement to fix these.
Probably not a lot, but might be worth doing.

The screenshot below is from a run of:

./debug -i -t1 -at -TF -sid -EG core-lib/Benchmarks/AsyncHarness.ns Savina.ForkJoinActorCreation 1000 0 40000