RFR: CODETOOLS-7903476: JMH: Threading model should not assume stable threads [v7]

[Aleksey Shipilev]

> See the bug for the original bug report.
> 
> This PR makes sure the harness code is able to work with different styles of executors, including the custom executor that always gives us a new thread. Integration tests now run with several important executor modes to catch errors early.

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Adjust pre-integration tests
 - Merge branch 'master' into CODETOOLS-7903476-thread-models
 - More touchups
 - Wrap more things in privileged blocks
 - Test configurations again
 - Do not test FJP_COMMON, test FJP instead
 - Wrap more things in privileged blocks
 - Working on proper test matrix
 - Drop --enable-preview from test config
 - Fixing GHA
 - ... and 1 more: https://git.openjdk.org/jmh/compare/3e54394f...6a063f0f

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Changes: https://git.openjdk.org/jmh/pull/107/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=107&range=06
  Stats: 581 lines in 26 files changed: 433 ins; 66 del; 82 mod
  Patch: https://git.openjdk.org/jmh/pull/107.diff
  Fetch: git fetch https://git.openjdk.org/jmh.git pull/107/head:pull/107

PR: https://git.openjdk.org/jmh/pull/107