RFR: 8332597: Remove redundant methods from j.l.classfile.ClassReader API [v2]

[Adam Sotona]

> j.l.classfile.ClassReader instance is exposed in the Class-File API through j.l.classfile.AttributeMapper::readAttribute method only.
> ClassReader only purpose is to serve as a tool for reading content of a custom attribute in a user-provided AttribtueMapper.
> It contains useful set of low-level class reading methods for user to implement a custom attribute content parser.
> 
> However methods ClassReader::thisClassPos and ClassReader::skipAttributeHolder are not necessary for a custom attribute content parsing and so redundant in the API.
> Class-File API implementation internally use these methods, however they should not be exposed in the API.
> 
> This patch removes the methods from the API.
> 
> Please review.
> 
> Thanks,
> Adam

Adam Sotona has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Merge branch 'master' into JDK-8332597-classreader-redundancy
   
   # Conflicts:
   #	src/java.base/share/classes/jdk/internal/classfile/impl/ClassImpl.java
 - 8332597: Remove redundant methods from j.l.classfile.ClassReader API

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Changes: https://git.openjdk.org/jdk/pull/19323/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19323&range=01
  Stats: 23 lines in 5 files changed: 0 ins; 17 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/19323.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19323/head:pull/19323

PR: https://git.openjdk.org/jdk/pull/19323