<i18n dev> RFR: 8316557: Make fields final in 'sun.util' package

[Andrey Turbanov]

A few classes in `sun.util` package have non-final fields which could easily be marked `final`.

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Commit messages:
 - [PATCH] Make fields final in 'sun.util' package

Changes: https://git.openjdk.org/jdk/pull/15736/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15736&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316557
  Stats: 42 lines in 10 files changed: 2 ins; 13 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/15736.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15736/head:pull/15736

PR: https://git.openjdk.org/jdk/pull/15736