RFR: 8319761: Simplify fields of Array VarHandles

[Chen Liang]

1. Primitive array VHs are now singletons and no longer need to record their array base and offset in their object themselves.
2. Moved Unsafe offset calculation to a utility method, like `index` in VarHandleByteArrayView.

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Commit messages:
 - Use the base offset and index scale constants from Unsafe directly
 - Simplify non-Object array VH

Changes: https://git.openjdk.org/jdk/pull/15894/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15894&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319761
  Stats: 147 lines in 3 files changed: 45 ins; 37 del; 65 mod
  Patch: https://git.openjdk.org/jdk/pull/15894.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15894/head:pull/15894

PR: https://git.openjdk.org/jdk/pull/15894