RFR: Move BiasedLocking and general mark preservation to prolog/epilog

[Roman Kennke]

That seems better indeed. Thanks!
Roman


> http://cr.openjdk.java.net/~shade/shenandoah/nofwdptr-mc-marks/webrev.01/
> 
> Another this spotted in sh/jdk: preserved marks preparation/restoration is not at the same nesting
> level in mark-compact. It is cleaner to have them near each other in more "general" prolog/epilog
> sections.
> 
> Testing: hotspot_gc_shenadoah
>