RFR: 7904033: jcstress: Upgrade Unsafe tests to use VarHandles [v2]

[Aleksey Shipilev]

> With Unsafe being deprecated, we need to rewrite some of the tests to VarHandles.
> 
> Public samples and fences tests have been rewritten to VarHandles. VarHandle fences are simple wrappers over Unsafe, we expect no surprises. Other tests were copied and reimplemented with VarHandles to still have more coverage for Unsafe paths, until Unsafe is completely removed.

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Touchups

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Changes:
  - all: https://git.openjdk.org/jcstress/pull/166/files
  - new: https://git.openjdk.org/jcstress/pull/166/files/bfd3edfd..8a2328cc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jcstress&pr=166&range=01
 - incr: https://webrevs.openjdk.org/?repo=jcstress&pr=166&range=00-01

  Stats: 9 lines in 9 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jcstress/pull/166.diff
  Fetch: git fetch https://git.openjdk.org/jcstress.git pull/166/head:pull/166

PR: https://git.openjdk.org/jcstress/pull/166