RFR: 8308642: Unhelpful pattern switch error: illegal fall-through to a pattern

[Aggelos Biboudis]

Improves two error messages regarding fall-through.

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Commit messages:
 - 8308642: Unhelpful pattern switch error: illegal fall-through to a pattern

Changes: https://git.openjdk.org/jdk/pull/19361/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19361&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308642
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19361.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19361/head:pull/19361

PR: https://git.openjdk.org/jdk/pull/19361