RFR: Fix mark-preserving in ShenandoahMarkCompact

[Roman Kennke]

CI found a bug in Shenandoah with eliminate-fwdptr-word applied: specjvm 
with +aggressive and +ShenandoahOOMDuringEvacALot would fail with 
mismatched locks.

The reason is that the mark-preserving in mark-compact has a few issues:
- It lacked preserving marks for humongous objects
- It lacked BiasedLocking::preserve_marks() / restore_marks()
- It used must_be_preserved() instead of 
must_be_preserved_for_promotion_failure(), the latter deals with biased 
locks a little differently (and I think correctly for our purpose).

All those issues are addressed in the patch. I switched from self-made 
mark-preserving to using gc/shared/preservedMarks.hpp which has the 
additional advantage that I don't have to resort to locking to protect 
the datastructures, and can instead use one stack per worker to record 
and restore marks.

http://cr.openjdk.java.net/~rkennke/fixpreservemark/webrev.00/

Testing: hotspot_gc_shenandoah, the failing specjvm test multiple times

Ok?

Thanks,
Roman