RFR: 8374749: Clarify AnnotationValue specification

[Joe Darcy]

Make the correspondence between AnnotationValue cases and the cases listed in JLS 9.6.1 more explicit.

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Commit messages:
 - JDK-8374749: Clarify AnnotationValue specification

Changes: https://git.openjdk.org/jdk/pull/29101/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29101&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374749
  Stats: 11 lines in 2 files changed: 2 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/29101.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29101/head:pull/29101

PR: https://git.openjdk.org/jdk/pull/29101