RFR: 8319463: ClassSignature should have superclass and superinterfaces as ClassTypeSig

Mon Nov 6 06:47:30 UTC 2023

Discovered while writing a test for #16513 that `ClassSignature.superclassSignature()` does not return a `ClassTypeSig`, yet [JVM Spec](https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-4.html#jvms-4.7.9.1-4100) requires it to be one. This patch adds such a requirement to the accessors, factories, and the parsing logic.

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Commit messages:
 - 8319463: ClassSignature should have superclass and superinterfaces as ClassTypeSig

Changes: https://git.openjdk.org/jdk/pull/16514/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16514&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319463
  Stats: 22 lines in 3 files changed: 8 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/16514.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16514/head:pull/16514

PR: https://git.openjdk.org/jdk/pull/16514