RFR: 8316641: VarHandle template classes can share code in the base class [v2]

[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 incrementally with one additional commit since the last revision:

  byte array var handles can share a common base class

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15854/files
  - new: https://git.openjdk.org/jdk/pull/15854/files/3a73e9ad..12404165

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15854&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15854&range=00-01

  Stats: 74 lines in 4 files changed: 32 ins; 34 del; 8 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