RFR: 8309595: Allow javadoc to process unnamed classes

[Jim Laskey]

Unnamed classes are rejected by javadoc because they are synthetic.

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Commit messages:
 - Backport 0be39054a631f282acc7ea05b2d98878a2b250bf

Changes: https://git.openjdk.org/jdk21/pull/1/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=1&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309595
  Stats: 87 lines in 3 files changed: 86 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21/pull/1.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/1/head:pull/1

PR: https://git.openjdk.org/jdk21/pull/1