RFR (XXS) 8037295: Add size_t versions of Atomic::add, dec, and inc

[David Simms]

Gidday,

Some folks have requested size_t type variants of Atomic add, dec and 
inc; to save on messy looking casts or using an inappropriate type.

Bug/Enhancement: https://bugs.openjdk.java.net/browse/JDK-8037295

Webrev: http://cr.openjdk.java.net/~dsimms/8037295/ 
<http://cr.openjdk.java.net/%7Edsimms/8037295/>

Have searched for existing cases, most looked like a potential change in 
type size or requiring const (still needs cast), except for 
heapRegionRemSet.hpp where size_t was clearly the intended type.

Testing: hotspot jtreg tests and "quick test list".

Cheers
/David Simms