Finder framework should suggest places for using private interface methods in lieu of private nested classes

With the release of https://bugs.openjdk.java.net/browse/JDK-8071453, JDK's own code
base could begin taking advantage of the new capability to use private methods in interfaces.
In the absence of such capability till date, programmers have had to resort to awkward and
clumsy workarounds such as having to create a private nested class to park such methods.

This ticket is to request an enhancement to the finder framework in javac to issue diagnostics
indicating places where such private nested class usage could be replaced with the more direct
private interface methods approach.