RFR: 8327501: Common ForkJoinPool prevents class unloading in some cases

[Viktor Klang]

creating threads in the common ForkJoinPool preventing class unloading. This fix avoids that when no SecurityManager is configured.

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

Commit messages:
 - Addresses a capture of AccessControlContext when

Changes: https://git.openjdk.org/jdk/pull/18144/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18144&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327501
  Stats: 6 lines in 1 file changed: 3 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18144.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18144/head:pull/18144

PR: https://git.openjdk.org/jdk/pull/18144