RFR: 8316641: VarHandle template classes can share code in the base class [v8]

[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 two commits:

 - Merge branch 'master' of https://github.com/openjdk/jdk into cleanup/vh-template-share
 - 8316641: VarHandle template classes can share code in the base class

-------------

Changes: https://git.openjdk.org/jdk/pull/15854/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15854&range=07
  Stats: 200 lines in 7 files changed: 57 ins; 79 del; 64 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