[6.x] Replace currency and country dictionaries with Symfony Intl CLDR data

[jasonvarga]

Summary

• The Currencies dictionary now pulls its item list from Symfony\Component\Intl\Currencies, keeping the same item shape and option labels. Hand-maintained lang/*/dictionary-currencies.php files are removed, and the translator script no longer treats that file as manual.
• The Countries dictionary now pulls names and alpha-3 codes from Symfony\Component\Intl\Countries. A small subregion => [iso2, …] map declared on the class preserves the region filter config and the subregion/region item fields. Flag emojis are derived from the alpha-2 code via Unicode regional indicator math. The 250 hand-translated country names per locale are removed from lang/*/dictionary-countries.php; the regions/subregions labels are kept.
• Sorting for countries uses Str::ascii() as the sort key, so accented names (Åland, Côte d'Ivoire, Réunion, São Tomé) collate alongside their ASCII counterparts rather than landing after Z under byte-wise comparison.
• Antarctica, Bouvet Island, and Heard & McDonald Islands no longer have a region assignment, and the (non-standard) polar region is removed from the filter options. Kosovo is dropped since it isn't in Symfony's list.
• Tests are reshaped in a stable style: assert spot-check entries where the English name is stable, use Str::ascii()-aware subset assertions for search, and exercise locale-aware naming via app()->setLocale('de').

Notable label changes

Because CLDR is the source of truth, English names shift slightly toward standardized Unicode spellings — e.g. "Aland Islands" → "Åland Islands", "Ivory Coast" → "Côte d'Ivoire", "Virgin Islands (US)" → "U.S. Virgin Islands", "Antigua And Barbuda" → "Antigua & Barbuda", "Macau S.A.R." → "Macao SAR China".

Test plan

• ./vendor/bin/phpunit tests/Dictionaries/ passes
• ./vendor/bin/phpunit tests/Fieldtypes/DictionaryTest.php tests/Fieldtypes/DictionaryFieldsTest.php passes
• ./vendor/bin/phpunit tests/Feature/GraphQL/Fieldtypes/DictionaryFieldtypeTest.php tests/Tags/Dictionary/DictionaryTagTest.php passes
• ./vendor/bin/pint clean on changed files
• Manually exercise the Countries and Currencies dictionary fieldtypes in the Control Panel (region filter, emoji toggle, search, localized labels)

[jasonvarga]

This requires the intl extension which we can't introduce mid-way through 6.x.