RFR: 8202642: Replace PAR_OOP_ITERATE with templates

[Stefan Karlsson]

Hi all,

Please review this patch to replace the PAR_OOP_ITERATE macros with 
templates.

http://cr.openjdk.java.net/~stefank/8202642/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8202642

The macros require use to stamp out GC-specific closures in shared code, 
while templates allows us to contain the GC-specific code in the 
GC-specific directories.

This patch builds upon the patch in:
http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-May/021968.html

Thanks,
StefanK