RFR: 8314261: Make fields final in sun.net.www

[Andrey Turbanov]

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

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Commit messages:
 - [PATCH] Make fields final in sun.net.www
 - [PATCH] Make fields final in sun.net.www

Changes: https://git.openjdk.org/jdk/pull/14977/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14977&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314261
  Stats: 58 lines in 13 files changed: 3 ins; 8 del; 47 mod
  Patch: https://git.openjdk.org/jdk/pull/14977.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14977/head:pull/14977

PR: https://git.openjdk.org/jdk/pull/14977