RFR: 8342707: Prepare Gatherers for graduation from Preview [v3]

[Viktor Klang]

> Make final adjustments to drop PreviewFeature and updating the @ since markers.

Viktor Klang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Updating copyright years and removing an unneccessary import for Gatherers
 - Removing PreviewFeature from Gatherers
 - Updating @since to 24 for Gatherers

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Changes: https://git.openjdk.org/jdk/pull/21686/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21686&range=02
  Stats: 39 lines in 24 files changed: 0 ins; 19 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/21686.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21686/head:pull/21686

PR: https://git.openjdk.org/jdk/pull/21686