<i18n dev> RFR: 8311188: Simplify and modernize equals and hashCode in java.text

[Pavel Rappo]

Please review this PR to use modern APIs and language features to simplify `equals` and `hashCode` in the java.text area.

* Some changes to `equals` and `hashCode` are refactoring rather than modernization. Such changes can be as trivial as rearranging, adding, or commenting checks.

* java.text area contains more classes whose `equals` and `hashCode` could be simplified; for example: sun.text.CompactByteArray or java.text.DigitList. However, I found no evidence of `equals` and `hashCode` in those classes being used in source or tests. Since writing new tests in this case seems unreasonable, I **excluded** those classes from this PR.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/14752/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14752&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311188
  Stats: 121 lines in 15 files changed: 31 ins; 52 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/14752.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14752/head:pull/14752

PR: https://git.openjdk.org/jdk/pull/14752