RFR: 8229485: Add decrementExact(), incrementExact(), and negateExact() to java.lang.StrictMath

[Julia Boes]

Hi,

This fix adds decrementExact(), incrementExact(), and negateExact() to 
java.lang.StrictMath. The methods were added to java.lang.Math 
previously [1] and should have been added to java.lang.StrictMath for 
consistency.

Bug: https://bugs.openjdk.java.net/browse/JDK-8229485

Webrev: http://cr.openjdk.java.net/~dfuchs/jboes/8229485/webrev.01/

CSR: https://bugs.openjdk.java.net/browse/JDK-8229702

Thanks,

Julia

[1] https://bugs.openjdk.java.net/browse/JDK-8022109