RFR 8249837: Avoid direct or implicit Thread::current() calls when we already have a current thread variable

[coleen.phillimore at oracle.com]

Summary: Add current thread and/or moved HandleMark to the scope that it 
is needed

This patch removes HandleMarks from the GC code.  I added a NoHandleMark 
to these places and found the locations in the verification code that 
needs the HandleMarks, and moved them there.

Tested with tier1-6 with no failures.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8249837.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8249837

Thanks,
Coleen