RFR (S) 8223446: Shenandoah breaks alignment with some HumongousThreshold values

[Roman Kennke]

Looks good, thank you!

Roman


> Bug:
>    https://bugs.openjdk.java.net/browse/JDK-8223446
> 
> HumongousThreshold is not aligned to MinObjAlignment. Since HumongousThreshold drives the
> MaxTLABSize, issuing such max-sized TLAB would leave allocation top unaligned. This readily
> manifests on x86_32. x86_64 is more or less safe as default alignment matches the single HeapWord.
> 
> Fix:
>    http://cr.openjdk.java.net/~shade/8223446/webrev.01/
> 
> This aligns all affected values, adds asserts, makes some computations use multiplication rather
> than division to avoid awkward precision issues, and extends the test to capture more problems.
> 
> Testing: hotspot_gc_shenandoah (x86_32, x86_64)
>