Adds one test covering the currentLocale / defaultLocale /
availableLocales getters on the I18n class. Existing suite exercised
the lookup behaviour but never read back the three locale fields,
leaving them as the last reachable gaps in lib/kernel/src/i18n/.
Coverage: kernel/src/i18n/i18n.dart 54/58 -> 57/58. The 1 remaining
line is the I18nReplacer const-constructor body (lcov phantom).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.7
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