RFR: 8314129: Make fields final in java.util.Scanner

[Andrey Turbanov]

Made a few fields `final` in java.util.Scanner.
Also made `digits`, `non0Digit`, `SIMPLE_GROUP_INDEX` as `static.`

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Commit messages:
 - [PATHC] Make fields final in java.util.Scanner

Changes: https://git.openjdk.org/jdk/pull/14863/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14863&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314129
  Stats: 34 lines in 1 file changed: 17 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/14863.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14863/head:pull/14863

PR: https://git.openjdk.org/jdk/pull/14863