RFR: 8322732: ForkJoinPool may underutilize cores in async mode

[Doug Lea]

This set of changes address causes of poor utilization with small numbers of cores due to overly aggressive contention avoidance. A number of further adjustments were needed to still avoid most contention effects in deployments with large numbers of cores

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Commit messages:
 - Merge branch 'openjdk:master' into JDK-8322732
 - Repack some fields; adjust control flow
 - Merge branch 'openjdk:master' into JDK-8322732
 - Next version
 - Merge branch 'openjdk:master' into JDK-8322732
 - Reduce unneeded signals
 - Merge branch 'openjdk:master' into JDK-8322732
 - reduce memory contention
 - Merge branch 'openjdk:master' into JDK-8322732
 - re-integrate docs
 - ... and 23 more: https://git.openjdk.org/jdk/compare/f12ed061...7e64cdfc

Changes: https://git.openjdk.org/jdk/pull/19131/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322732
  Stats: 593 lines in 1 file changed: 162 ins; 159 del; 272 mod
  Patch: https://git.openjdk.org/jdk/pull/19131.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19131/head:pull/19131

PR: https://git.openjdk.org/jdk/pull/19131