RFR: 8342083: Make a few fields in FileSystemPreferences final

[Andrey Turbanov]

8342083: Make a few fields in FileSystemPreferences final

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Commit messages:
 - [PATCH] Make a few fields in FileSystemPreferences final

Changes: https://git.openjdk.org/jdk/pull/21131/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342083
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/21131.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21131/head:pull/21131

PR: https://git.openjdk.org/jdk/pull/21131