RFR: 8368331: ClassFile Signature parsing fails for type parameter with no supertype

[Chen Liang]

Some type parameter declaration signatures in class and method generic signatures, such as `<T:R:>`, are valid per JVMS but are not accepted by either the ClassFile or the legacy core reflection parser. (Javac doesn't generate these because it always generates an Object upper bound) They can be constructed by the ClassFile API models. So it makes sense to support their parsing as supported by JVMS and our API model.

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Depends on: https://git.openjdk.org/jdk/pull/27380

Commit messages:
 - 8368331: ClassFile Signature parsing fails for type parameter with no supertype

Changes: https://git.openjdk.org/jdk/pull/27439/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27439&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368331
  Stats: 31 lines in 2 files changed: 28 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27439.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27439/head:pull/27439

PR: https://git.openjdk.org/jdk/pull/27439