RFR: 8316641: VarHandle template classes can share code in the base class [v4]

[Chen Liang]

> VarHandle implementations have many static fields and methods that can be pulled to the common superclass to avoid repeated initialization and code duplication.
> 
> In addition, the Unsafe-based Buffer field access are replaced by usage of public methods or JavaNioAccess.

Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'pr/15103' of https://github.com/openjdk/jdk into cleanup/vh-template-share
 - Post-merge cleanup
 - Merge branch 'pr/15103' of https://github.com/openjdk/jdk into cleanup/vh-template-share
 - byte array var handles can share a common base class
 - Clean up VarHandle template classes

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Changes: https://git.openjdk.org/jdk/pull/15854/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15854&range=03
  Stats: 203 lines in 7 files changed: 58 ins; 79 del; 66 mod
  Patch: https://git.openjdk.org/jdk/pull/15854.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15854/head:pull/15854

PR: https://git.openjdk.org/jdk/pull/15854