[jdk21u-dev] RFR: 8314578: Non-verifiable code is emitted when two guards declare pattern variables in colon-switch

[Aleksey Shipilev]

Clean backport to resolve javac compilation bug.

Additional testing:
 - [x] New test fails without the fix, passes with it
 - [x] `langtools_all` passes

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Commit messages:
 - Backport 15588e08ed455eac356aa923c35503beaecd5b6d

Changes: https://git.openjdk.org/jdk21u-dev/pull/26/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=26&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314578
  Stats: 52 lines in 3 files changed: 49 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/26.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/26/head:pull/26

PR: https://git.openjdk.org/jdk21u-dev/pull/26