LibUnicode: Add lexer to test if a string matches the "type" production

Author: https://github.com/trflynn89
Commit: a05419db55
Pull-request: https://github.com/SerenityOS/serenity/pull/9749
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibUnicode/Locale.h

@@ -62,6 +62,7 @@ bool is_unicode_language_subtag(StringView);
 bool is_unicode_script_subtag(StringView);
 bool is_unicode_region_subtag(StringView);
 bool is_unicode_variant_subtag(StringView);
+bool is_type_identifier(StringView);
 
 Optional<LanguageID> parse_unicode_language_id(StringView);
 Optional<LocaleID> parse_unicode_locale_id(StringView);