RFR: 8365699: Remove jdk.internal.javac.PreviewFeature.Feature enum values for features finalized in Java 25 or earlier

[Jaikiran Pai]

Can I please get a review of this change which cleans up the outdated enum constants in the internal `jdk.internal.javac.PreviewFeature$Feature` enum?

This addresses https://bugs.openjdk.org/browse/JDK-8365699. As noted in that issue, this enum has accumulated some outdated preview feature constants which are no longer needed. The changes in this PR removes those enum constants whose preview features have been finalized in Java 25 or earlier (the current mainline bootstrap JDK is Java 25). A code comment explaining the lifetime of these enum constants has also been added.

No new tests have been introduced and tier1, tier2, tier3 testing is currently in progress in the CI.

-------------

Commit messages:
 - 8365699: Remove jdk.internal.javac.PreviewFeature.Feature enum values for features finalized in Java 25 or earlier

Changes: https://git.openjdk.org/jdk/pull/28128/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28128&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365699
  Stats: 23 lines in 1 file changed: 15 ins; 6 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28128.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28128/head:pull/28128

PR: https://git.openjdk.org/jdk/pull/28128