RFR: 8366094: Sealed graph for nested types creates broken links

[Hannes Wallnöfer]

Please review a change to fix broken links in sealed type hierarchy graphs for nested types. The problem is that enclosing types are included in the path of the graph file and therefore must have a matching `../` in the generated link. 

Fixed graphs for some nested sealed types: 
 - [ClassFile.Option](https://cr.openjdk.org/~hannesw/8366094/api.00/java.base/java/lang/classfile/ClassFile.Option.html)
 - [Signature.RefTypeSig](https://cr.openjdk.org/~hannesw/8366094/api.00/java.base/java/lang/classfile/Signature.RefTypeSig.html)
 - [TypeAnnotation.TargetInfo](https://cr.openjdk.org/~hannesw/8366094/api.00/java.base/java/lang/classfile/TypeAnnotation.TargetInfo.html)

There is currently no test coverage for the sealed graph taglet. I tested the fix manually, a test should be added with [JDK-8366828](https://bugs.openjdk.org/browse/JDK-8366828).

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Commit messages:
 - 8366094: Sealed graph for nested types creates broken links

Changes: https://git.openjdk.org/jdk/pull/28134/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28134&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366094
  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28134.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28134/head:pull/28134

PR: https://git.openjdk.org/jdk/pull/28134