RFR: 8344773: SM cleanup in ForkJoinPool [v2]

[Doug Lea]

> Complete the SM cleanup in java.util.concurrent that was deferred during other FJP updates

Doug Lea has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8344773
 - Remove redundant doc comment; clarify condinional
 - Merge branch 'openjdk:master' into JDK-8344773
 - Remove SecurityManager-related code; refactor resetThreadLocals

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22324/files
  - new: https://git.openjdk.org/jdk/pull/22324/files/fb756fae..12126ed1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22324&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22324&range=00-01

  Stats: 10062 lines in 127 files changed: 9326 ins; 570 del; 166 mod
  Patch: https://git.openjdk.org/jdk/pull/22324.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22324/head:pull/22324

PR: https://git.openjdk.org/jdk/pull/22324