RFR: 8246429: Javadoc comparators are not module-aware

[Hannes Wallnoefer]

Please review: 

JBS: https://bugs.openjdk.java.net/browse/JDK-8246429
Webrev: http://cr.openjdk.java.net/~hannesw/8246429/webrev.00/

I originally fixed this as part of 8198705: Javadoc search needs a fix to handle duplicate package names in different modules, but it is a distinct issue so I filed a separate bug for it.

The fix adds an additional final step to element comparisons, which is to compare the name of the modules containing the elements. So far the final step in most comparators was to compare the fully qualified name of the elements.

Hannes