RFR: 8315974: Make fields final in 'com.sun.crypto.provider' package

[Andrey Turbanov]

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

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Commit messages:
 - [PATCH]: Make fields final in com.sun.crypto.provider package

Changes: https://git.openjdk.org/jdk/pull/15412/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15412&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315974
  Stats: 116 lines in 33 files changed: 6 ins; 6 del; 104 mod
  Patch: https://git.openjdk.org/jdk/pull/15412.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15412/head:pull/15412

PR: https://git.openjdk.org/jdk/pull/15412