RFR (S) 8237821: Shenandoah: build broken after JDK-8237637 (Remove dubious type conversions from oop)

[Roman Kennke]

Ok, that looks good.

Make sure you update copyright headers as appropriate.

Thank you!
Roman


> Bug:
>   https://bugs.openjdk.java.net/browse/JDK-8237821
> 
> Current release build in jdk/jdk is broken because of this. Instead of reverting the 8237637, let's
> complete the Shenandoah parts.
> 
> I believe it is in the spirit of the original patch to be explicit about oop/HeapWord*/void* in
> Shenandoah. cset->is_in(oop) should be doing the proper cast_from_oop dance that would go through
> CHECK_UNHANDLED_OOPS and friends. So we need an overload to handle potentially interior pointers
> (HeapWord*/void*). And it also removes some of the template mess we have, that lead to this failure.
> 
> Fix:
>   https://cr.openjdk.java.net/~shade/8237821/webrev.01
> 
> Testing: Linux x86_64 {release,fastdebug,slowdebug} hotspot_gc_shenandoah
>