RFR: JDK-8261079: Fix support for @hidden in classes and interfaces [v4]

[Hannes Wallnöfer]

> This change improves support for the `@hidden` tag to suppress documentation for specific elements, especially in the context of classes, interfaces and inheritance/method overriding.
> 
> The important changes are in `Utils` and in `VisibleMemberTable`. (There is also a number of non-related small code cleanup changes, sorry about that, I know it makes review a bit harder but I couldn't resist.)
> 
> In `Utils` the most important change are:
> 
>  - Consider types as "undocumented enclosures" if they are marked with a `@hidden` tag
>  - Check for `@hidden` tags even in non-included elements as they may be included via undocumented enclosures
>  - To counter the above change, only run doclint on elements that are either included or contained in an included type, as we don't want to report warnings or errors for non-included code. 
>  
> In `VisibleMemberTable` there is a subtle change to not consider an overriding method as a "simple override" if the overridden method is hidden or otherwise invisible but in turn is a non-simple override of a method further up the inheritance chain. This resulted in methods which should have been documented as declared locally to be documented as declared in supertypes. I also did a bit of renaming in `VisibleMemberTable` to make the purpose of things a bit clearer.
> 
> Other than that, most of the changes consist of added calls to `utils.hasHiddenTag(Element)`, usually with the purpose of not generating links to things that are not there.

Hannes Wallnöfer has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8261079: Remove unnecessary isSelected check

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2406/files
  - new: https://git.openjdk.java.net/jdk/pull/2406/files/9760a32d..66e9b54a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2406&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2406&range=02-03

  Stats: 5 lines in 1 file changed: 1 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2406.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2406/head:pull/2406

PR: https://git.openjdk.java.net/jdk/pull/2406