<i18n dev> RFR: 8317979: Use TZ database style abbreviations in the CLDR locale provider

[Naoto Sato]

CLDR provides very few short names for time zones, such as PST/PDT. This will typically end up substituting names from the COMPAT provider. Once the COMPAT is removed, they will be displayed in the GMT format, i.e., GMT+XX:YY. Although some of the short names in the COMPAT provider are somewhat questionable (less common ones are simply made up from the long names by taking the initials), it would not be desirable for them to fall back to the GMT format.
To mitigate the situation, CLDR can use the abbreviated names from the TZ database, which contains legacy (major) short names as FORMAT. The CLDR provider can use them instead of the GMT offset style. This enhancement is a precursor to the future removal of the COMPAT provider.

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Commit messages:
 - tidy up
 - substitute letters
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/16206/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16206&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317979
  Stats: 162 lines in 6 files changed: 139 ins; 1 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/16206.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16206/head:pull/16206

PR: https://git.openjdk.org/jdk/pull/16206