RFR: 8349512: Duplicate PermittedSubclasses entries with doclint enabled

Fri Feb 7 00:36:34 UTC 2025

This change avoids emitting duplicate `PermittedSubclasses` entries when `-Xdoclint` is enabled.

`-Xdoclint` causes some trees to be re-attributed, and the second attribution was resulting in permitted subclasses being added again, and those side effects were not discarded. This fix causes `addPermittedSubclass` to not insert duplicate entries.

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Commit messages:
 - 8349512: Duplicate PermittedSubclasses entries with doclint enabled

Changes: https://git.openjdk.org/jdk/pull/23507/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23507&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349512
  Stats: 35 lines in 2 files changed: 33 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23507.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23507/head:pull/23507

PR: https://git.openjdk.org/jdk/pull/23507