[11u] RFR/RFC: Bulk backport to sh/jdk11

[Roman Kennke]

Ok looks good.
I'm taking care of remaining non-LRB backports. Sorry, I'm a bit slow
today, kids making troubles...

Cheers,
Roman


> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20190516/webrev.01/
> 
> This bunch includes:
> 
>  8223980: Shenandoah: Refactor and fix ObjArrayChunkedTask verification
>  8223762: Shenandoah: overflows in calculations involving heap capacity
>  8223759: Shenandoah should allow arbitrarily low initial heap size
>  8223427: [TESTBUG] Disable JTReg Shenandoah tests when Graal is enabled
>  8223447: Stabilize gc/shenandoah/TestStringDedupStress test
>  8223446: Shenandoah breaks alignment with some HumongousThreshold values
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release}, also with Graal enabled
>