RFR: 8237383: Members inherited from non-public types are not included in index

[Hannes Wallnöfer]

Please review: 

JBS: https://bugs.openjdk.java.net/browse/JDK-8237383
Webrev: http://cr.openjdk.java.net/~hannesw/8237383/webrev.00/

This patch makes sure members inherited from non-documented parents are included in HTML and search index files.

There is a new IndexItem class to the doclets.toolkit.util package that is used instead of raw Elements to collect indexed elements by IndexBuilder. This is necessary because we need to know the inheriting class when rendering a member signature as the member type may change by instantiating type parameters. 

IndexItem can also hold a SearchIndexItem so that index tags can be added to IndexBuilder to generate index files from a single collection rather than manually merging two collections.

Unfortunately I ran into some obstacles with this, so the resulting code is not quite as simple and unified as I would have liked. HTML and search indexes are structured differently and each use a variety of different formats and comparators for sorting. This makes it very difficult to manage everything within a single place, so there’s still much of the original redundancy and complexity left.

I also moved all comparator factory methods from the Utils class to a new Comparators class. The code is mostly unchanged as I was not able to simplify it without changing behaviour. There is one new comparator factory method that generates a composite generator for the IndexItems containing elements and search tags in the HTML index. 

The changes in VisibleMemberTree are mostly removal of dead code. The implementation of getExtraMembers(Kind) was the same as getAllVisibleMembers(Kind), so no additional members were found and added by that method. There is also a bit of code cleanup in that class.


Thanks,
Hannes