[jdk25u-dev] RFR: 8368500: ContextClassLoader cannot be reset on threads in ForkJoinPool.commonPool()

[Roland Mesde]

Backporting JDK-8368500: ContextClassLoader cannot be reset on threads in ForkJoinPool.commonPool()

For parity with Oracle JDK.

With the Security Manager permanently disabled in JDK 24, setCCL allows setting a custom context class loader but prevents resetting it back to the system class loader before executing subsequent task code. This change relaxes the restriction to allow resetting to the system class loader.

Ran GHA Sanity Checks (passed), jtreg tier1 tests (passed) and related tests (passed) on linux-x64, linux-aarch64, macos-aarch64 and windows-x64:

(Passed) - make test-tier1
(Passed) - make test TEST=test/jdk/java/util/concurrent/forkjoin/ContextClassLoaderTest.java

Results are attached.

[linux-aarch64-jtreg-tier1.log](https://github.com/user-attachments/files/23941590/linux-aarch64-jtreg-tier1.log)
[linux-aarch64-specific-test.log](https://github.com/user-attachments/files/23941591/linux-aarch64-specific-test.log)
[linux-x64-jtreg-tier1.log](https://github.com/user-attachments/files/23941592/linux-x64-jtreg-tier1.log)
[linux-x64-specific-test.log](https://github.com/user-attachments/files/23941594/linux-x64-specific-test.log)
[macos-aarch64-jtreg-tier1.log](https://github.com/user-attachments/files/23941596/macos-aarch64-jtreg-tier1.log)
[macos-aarch64-specific-test.log](https://github.com/user-attachments/files/23941597/macos-aarch64-specific-test.log)
[windows-x64-specific-test.log](https://github.com/user-attachments/files/23941598/windows-x64-specific-test.log)

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Commit messages:
 - Backport 6f8d07ae21e49f87f64a5d4e10c930c4447ec8b6

Changes: https://git.openjdk.org/jdk25u-dev/pull/65/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u-dev&pr=65&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368500
  Stats: 60 lines in 2 files changed: 56 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk25u-dev/pull/65.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u-dev.git pull/65/head:pull/65

PR: https://git.openjdk.org/jdk25u-dev/pull/65