RFR: 8314423: Multiple patterns without unnamed variables [v2]

[Aggelos Biboudis]

> This PR addresses both [JDK-8314423](https://bugs.openjdk.org/browse/JDK-8314423) and [JDK-8314216](https://bugs.openjdk.org/browse/JDK-8314216), since both are relevant to checks around the structure of switch in the relevant method in `Check`. Additionally a check was needed in `analyzePattern` to detect that when a case starts with a constant case label followed by a `,` or `->` is indeed a constant expression and not a pattern as previously signified.

Aggelos Biboudis has updated the pull request incrementally with one additional commit since the last revision:

  Cleanup of T8314216

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15310/files
  - new: https://git.openjdk.org/jdk/pull/15310/files/6fa8619b..07308ba2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15310&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15310&range=00-01

  Stats: 6 lines in 2 files changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15310.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15310/head:pull/15310

PR: https://git.openjdk.org/jdk/pull/15310