[jdk21u-dev] RFR: 8351458: (ch) Move preClose to UnixDispatcher

[Shruthi Acharya]

OpenJDK PR: https://github.com/openjdk/jdk/pull/23956
OpenJDK bug: https://bugs.openjdk.org/browse/JDK-8351458

The original patch didn’t apply cleanly to the JDK21u-dev branch due to a copyright header mismatch. However, the rest of the changes were ported without issues. Manually updated the copyright header to resolve the conflict.

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Commit messages:
 - Backport 0de2cddf3a7be23f67af93972875af1235f3107e

Changes: https://git.openjdk.org/jdk21u-dev/pull/2051/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2051&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351458
  Stats: 163 lines in 12 files changed: 43 ins; 82 del; 38 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2051.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2051/head:pull/2051

PR: https://git.openjdk.org/jdk21u-dev/pull/2051