SimpleVisitors and Scanners in jdk.compiler should use @implSpec

Summary

Specifications of jdk.compiler's DocTreeScanner, SimpleDocTreeVisitor, SimpleTreeVisitor and TreeScanner are enhanced by adding @implSpec javadoc tag.

Problem

Most methods in jdk.compiler's DocTreeScanner, SimpleDocTreeVisitor, SimpleTreeVisitor and TreeScanner specify the implementation's behavior, but don't use @implSpec tag. A few methods fail to override the javadoc and specify the implementation behavior. The DocTreeScanner class' javadoc also has a specification on implementations, but does not use @implSpec tag.

Solution

Methods in the specified classes are enhanced to use @implSpec. javadoc is added in cases it is missing. DocTreeScanner's javadoc is enhanced to use @implSpec.

Specification

Please see the attached specdiff.01.zip, also available for convenience here: http://cr.openjdk.java.net/~jlahoda/8267832/specdiff.01/overview-summary.html