<i18n dev> RFR: 5066247: Refine the spec of equals() and hashCode() for j.text.Format classes

[Justin Lu]

Please review this PR which refines the spec of `equals()` and `hashCode()` in `java.text.Format` related classes.

The current spec for most of these methods is either  "_Overrides <method_name>_" or are incomplete/wrong (i.e. see `ChoiceFormat`).

This fix adjusts the spec to provide a consistent definition for the overridden methods and specify what is being compared/used to generate a hash code value.

For implementations that use at most a few fields, the values are stated, otherwise a more general term is used as a substitution (i.e. see `DecimalFormat`).

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Commit messages:
 - Remove additional see tag from dFmt.hashCode()
 - Include CompactNumberFormat.java
 - Drop 'Obeys the general contract' wording and further standardizing
 - Touch up and standardize
 - Update rest of related classes
 - Adjust ChoiceFormat (refer to public method)
 - Update NumberFormat
 - Update DecimalFormat
 - Update DateFormat
 - Adjust ChoiceFormat
 - ... and 1 more: https://git.openjdk.org/jdk/compare/7c169a42...84bd4708

Changes: https://git.openjdk.org/jdk/pull/15459/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15459&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-5066247
  Stats: 117 lines in 9 files changed: 92 ins; 1 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/15459.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15459/head:pull/15459

PR: https://git.openjdk.org/jdk/pull/15459