RFR [sh/8u]: Backport elimination of forwarding pointer

[Roman Kennke]

Ha, and it missed the webrev link:

http://cr.openjdk.java.net/~rkennke/nofwdptr-sh8/webrev.00/

Roman

> Notice that I backported jdk11's gc/shared/preservedMarks.* stuff into
> gc_implementation/shenandoah for mark-compact.
> 
> Roman
> 
> 
>> This backports the elimination of the forwarding pointer. It's the two
>> changesets:
>>
>> [backport] 8224584: Shenandoah: Eliminate forwarding pointer word
>> [backport] 8223567: Rename ShenandoahBrooksPointer to ShenandoahForwarding
>>
>> It also reverts a whole lot of shared code changes all over the place.
>>
>> Testing: hotspot_gc_shenandoah (x86/aarch64), specjvm ongoing
>>
>> Can I please get a review?
>>
>> Thanks,
>> Roman
>>
>