JDK 9 RFR of 8050430: Provided new utility visitors supporting SourceVersion.RELEASE_9

[Joe Darcy]

Hello,

Please review my changes for

     8050430: Provided new utility visitors supporting 
SourceVersion.RELEASE_9
     http://cr.openjdk.java.net/~darcy/8050430.0/

A few items of note:

* As proposed, this change deprecates all the FooVisitor6 classes. This 
is meant to be consistent with making -source/-target 6 obsolete in 
javac in JDK 9.

* A few @SupportedSourceVersion annotations missed in earlier releases 
have been added

Otherwise, as of today, the FooVisitor9 classes are straightforward 
extensions of existing classes. I went through the langtools src and 
test directories and updated existing visitor usages as appropriate. A 
few more tests were added to the JavacTestingAbstractProcessor fold or 
were updated to use the facilities of JavacTestingAbstractProcessor more 
effectively, such as by subclassing the latest-version utility visitors 
in that class.

Thanks,

-Joe