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

[Aleksey Shipilev]

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

-- 
Thanks,
-Aleksey