RFR: 8342468: Improve API documentation for java.lang.classfile.constantpool

[Chen Liang]

Improve documentation for constant pool entries.  This include some models for those entries, symbolic descriptors, and some general guidance in package summary.

APIDiff: https://cr.openjdk.org/~liach/apidiff/cf-consts/
Javadoc: https://cr.openjdk.org/~liach/javadoc/cf-consts/

Please review the associated CSR as well.

Companion PRs: #21625

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Commit messages:
 - Merge branch 'master' of https://github.com/openjdk/jdk into docs/cf-constantpool
 - More concise message about exceptions
 - Merge branch 'master' of https://github.com/openjdk/jdk into docs/cf-constantpool
 - Improve api docs for constantpool

Changes: https://git.openjdk.org/jdk/pull/22217/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22217&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342468
  Stats: 1114 lines in 30 files changed: 781 ins; 69 del; 264 mod
  Patch: https://git.openjdk.org/jdk/pull/22217.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22217/head:pull/22217

PR: https://git.openjdk.org/jdk/pull/22217