RFR: 8342466: Improve API documentation for java.lang.classfile.attribute [v2]

[Chen Liang]

> Improve documentation for `class` file attributes. This include better specification for user attributes, some more general information about attributes, such as the usage of non-JVMS attributes, and updated some attribute information in the base package too, such as Annotation and Signature.
> 
> APIDiff: https://cr.openjdk.org/~liach/apidiff/cf-attribute/
> Javadoc: https://cr.openjdk.org/~liach/javadoc/cf-attribute/java.base/java/lang/classfile/Attribute.html

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Review comments, also simplify Attribute

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23026/files
  - new: https://git.openjdk.org/jdk/pull/23026/files/575712c8..c08f76c0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23026&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23026&range=00-01

  Stats: 37 lines in 8 files changed: 5 ins; 12 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/23026.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23026/head:pull/23026

PR: https://git.openjdk.org/jdk/pull/23026