RFR: JDK-8309134: Augment test/langtools/tools/javac/versions/Versions.java for JDK 21 language changes [v2]

[Joe Darcy]

> Augment the Versions.java test in the usual way for new language changes.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback; increase coverage of negative test cases.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14229/files
  - new: https://git.openjdk.org/jdk/pull/14229/files/31dbd1ee..32879ef4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14229&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14229&range=00-01

  Stats: 17 lines in 1 file changed: 5 ins; 1 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/14229.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14229/head:pull/14229

PR: https://git.openjdk.org/jdk/pull/14229