RFR (S) 8249938: Move mirror oops from Universe into OopStorage

[coleen.phillimore at oracle.com]

Summary: Save and restore mirror oops to temporary array for CDS, and 
move them to OopStorage once restored.

This is a subtask of moving oops out of Universe.  I ran performance 
tested of this and there is no performance change.  Some slight decrease 
in number of instructions (improvement!) in Perfstartup-Noop that were 
flagged as significant - 0.10%

Tested with mach5 tier1-3.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8249938.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8249938

Thanks,
Coleen