RFR 10 JDK-8159995: Rename internal Unsafe.compare methods

[Ron Pressler]

Hi,
Please review the following core/hotspot change:

Bug: https://bugs.openjdk.java.net/browse/JDK-8159995
core webrev: 
http://cr.openjdk.java.net/~psandoz/jdk10/JDK-8159995-unsafe-compare-and-swap-to-set-jdk/webrev/
hotspot webrev: 
http://cr.openjdk.java.net/~psandoz/jdk10/JDK-8159995-unsafe-compare-and-swap-to-set-hotspot/webrev/

This change is covered by existing tests.

The following renaming was applied:

- compareAndExchange*Volatile -> compareAndExchange*
- compareAndSwap* -> compareAndSet*
- weakCompareAndSwap* -> weakCompareAndSet*Plain
- weakCompareAndSwap*Volatile -> weakCompareAndSet*

At this stage, only method and hotspot intrinsic names were changed; 
node names were left as-is, and may be handled in a separate issue.

Ron