RFR: 8336707: Contention of ForkJoinPool grows when stealing works

[Doug Lea]

This addresses tendencies in previous update to increase fencing, scanning, and signalling that can increase contention, and slow down performance especially on ARM platforms. It also uses more ARM-friendly constructions to reduce overhead (leading to several changes that all of the same form),

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Commit messages:
 - Consistent constructions; remove no-longer needed checks; update internal docs
 - Reconcile constuctions
 - Fencing
 - experiment
 - Merge branch 'openjdk:master' into JDK-8336707
 - Reactivation
 - Recheck
 - Uniform access expressions
 - Another diagnostic
 - More diagnostics
 - ... and 6 more: https://git.openjdk.org/jdk/compare/7312eea3...a1ad02fc

Changes: https://git.openjdk.org/jdk/pull/21507/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21507&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336707
  Stats: 288 lines in 1 file changed: 42 ins; 95 del; 151 mod
  Patch: https://git.openjdk.org/jdk/pull/21507.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21507/head:pull/21507

PR: https://git.openjdk.org/jdk/pull/21507