Use TZ database style abbreviations in the CLDR locale provider

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 the short names in the COMPAT provider are somewhat questionable (some less common ones are simply made up from the long names by taking the initials), it would be not desirable for them to fall back to 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.