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

[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.

-------------

Commit messages:
 - Fixing GHA
 - Fix

Changes: https://git.openjdk.org/jmh/pull/107/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=107&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903476
  Stats: 486 lines in 24 files changed: 358 ins; 65 del; 63 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