RFR: 8317937: @sealedGraph: Links to inner classes fails in links

[Chen Liang]

This fixes the links to nested classes like `ValueLayout.OfLong` in the rendered sealed class hierarchy graph.

A similar problem with nested classes exist for `@sealedGraph` on them, where their graphs will be generated to a wrong directory and the graph link broken, as seen in `StringTemplate.Processor.Linkage`. That will be done in a separate RFE.

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Commit messages:
 - 8317937: @sealedGraph: Links to inner classes fails in links

Changes: https://git.openjdk.org/jdk/pull/16292/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16292&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317937
  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16292.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16292/head:pull/16292

PR: https://git.openjdk.org/jdk/pull/16292