RFR: 8349512: Duplicate PermittedSubclasses entries with doclint enabled [v2]

[Liam Miller-Cushon]

> 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.

Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:

  Update @test with new bug ID

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23507/files
  - new: https://git.openjdk.org/jdk/pull/23507/files/d8a803f9..6143b762

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23507&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23507&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 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