RFR (S) 8242365: Shenandoah: use uint16_t instead of jushort for liveness cache

[Roman Kennke]

Looks good.

Thanks,
Roman


> RFE:
>   https://bugs.openjdk.java.net/browse/JDK-8242365
> 
> I was actually looking into this weird statement:
>   size_t max = (1 << (sizeof(jushort) * 8)) - 1;
> 
> ...which is borderline UB, because we can shift for more than datatype width. Then I figured we
> might as well replace jushort with uint16_t.
> 
> Webrev:
>   https://cr.openjdk.java.net/~shade/8242365/webrev.01/
> 
> Testing: hotspot_gc_shenandoah
>