RFR: 8331947: Preview creates checkbox for JEP-less preview feature

Wed May 22 08:43:25 UTC 2024

Please review a simple patch to exclude preview visitor classes meant to support future preview features from the Preview API page. 

The test adds an sample element annotated with the new `PreviewFeature.Feature.LANGUAGE_MODEL` constant (which does not have a `@JEP` annotation) to make sure it is not listed in the Preview API page. The test itself does not have to be modified, as it would fail without the change in `PreviewAPIListBuilder.java`.

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Commit messages:
 - JDK-8331947: Preview creates checkbox for JEP-less preview feature

Changes: https://git.openjdk.org/jdk/pull/19344/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19344&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331947
  Stats: 13 lines in 3 files changed: 9 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/19344.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19344/head:pull/19344

PR: https://git.openjdk.org/jdk/pull/19344