RFR 8247878: Move Management strong oops to OopStorage

[coleen.phillimore at oracle.com]

Summary: Use OopStorage for strong oops stored with memory and thread 
sampling and dumping, and remove oops_do and GC calls.

These use OopStorageSet::vm_global()  OopStorage for now.  I'll change 
the thread sampling oops to use a new OopStorage once the GC code is 
changed to nicely allow additional oop storages.  The memory pool oops 
are never deleted once created, so they should stay in vm_global() oop 
storage.

Tested with tiers 1-3 (tiers 4-6 with other changes) and 
javax/management tests.  I timed the tests to see if there was any 
noticeable performance difference, and there was not.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8247878.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8247878

Thanks,
Coleen