RFR: 8336781: Erroneous exhaustivity check with boolean switch

[Aggelos Biboudis]

In the case of a `Boolean` switch with 3 values true, false and `null` there was a miscalculation on what consists an exhaustive switch. This PR addresses this bug by removing the values true and false (instead of adding and comparing with 2 expected values).

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Commit messages:
 - 8336781: Erroneous exhaustivity check with boolean switch

Changes: https://git.openjdk.org/jdk/pull/20243/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336781
  Stats: 42 lines in 2 files changed: 39 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20243.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20243/head:pull/20243

PR: https://git.openjdk.org/jdk/pull/20243