[14] RFR (S) 8230853, 8237821: Shenandoah: replace leftover assert(is_in(...)) with rich asserts

[Roman Kennke]

Looks good to me.

Thanks,
Roman


> Original change:
>   https://bugs.openjdk.java.net/browse/JDK-8230853
>   https://hg.openjdk.java.net/jdk/jdk/rev/7e741a3fc650
> 
> We need JDK-8237821 change too, which introduced "oop" arguments:
>   https://cr.openjdk.java.net/~shade/8230853/webrev.14u.01/
> 
> This is already done in sh/jdk11:
>   https://hg.openjdk.java.net/shenandoah/jdk11/rev/ec859ee39571
> 
> Testing: hotspot_gc_shenandoah {fastdebug,release}, tier{1,2}
>