[lworld] RFR: 8351569: [lworld] Revisit atomic access modes in flat var handles [v2]

[Maurizio Cimadamore]

> This PR is an attempt to put var handle support for flat values on a more solid footing. Some more notes in a comment below.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Enhance compareAndSetFlatValueAsBytes to work on different kinds of flat arrays
  Cache result of oop-free analysis
  Beef up tests to check different combinations of VM flags

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1402/files
  - new: https://git.openjdk.org/valhalla/pull/1402/files/856cb9a0..8ca6bef1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1402&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1402&range=00-01

  Stats: 29 lines in 4 files changed: 13 ins; 1 del; 15 mod
  Patch: https://git.openjdk.org/valhalla/pull/1402.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1402/head:pull/1402

PR: https://git.openjdk.org/valhalla/pull/1402