RFR: 8329537: Nested and enclosing classes should be linked separately in breadcrumb navigation

[Hannes Wallnöfer]

Please review a patch to change the breadcrumb sub-navigation in API docs to display nested classes as separate links. 

The change itself is simple, I replaced the `getBreadCrumbLink` method in `HtmlDocletWriter` which returned a link for a single element with a new `addBreadCrumbLinks` method in `Navigation` which recursively adds all breadcrumb links to a list. Moving the code from `HtmlDocletWriter` to `Navigation` allowed me to remove a lot of code because it is no longer necessary to override the `getNavBar` method in a lot of writer subclasses.

I compared the JDI API documentation with and without this patch and there were no changes except for the breadcrumb links for nested classes.

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Commit messages:
 - JDK-8329537: Nested and enclosing classes should be linked separately in breadcrumb navigation

Changes: https://git.openjdk.org/jdk/pull/19466/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19466&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329537
  Stats: 196 lines in 10 files changed: 66 ins; 128 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19466.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19466/head:pull/19466

PR: https://git.openjdk.org/jdk/pull/19466