Fix invalid Unix locale to Flutter locale (BCP-47) mapping

Flutter locales use the BCP-47 format
(https://www.rfc-editor.org/rfc/bcp/bcp47.txt), and Unix locales use a POSIX
format. There is not a perfect mapping between them, see
https://wiki.openoffice.org/wiki/LocaleMapping

The current implementation is not correctly setting the appropriate optional
fields, so remove that.

There are likely some Unix locales that should set these fields, but these are
best fixed by adding special cases for them as they are discovered.

Fixes: flutter/flutter#111341

shell/platform/linux/fl_engine.cc

@@ -118,29 +118,23 @@ static void setup_locales(FlEngine* self) {
   // Helper array to take ownership of the strings passed to Flutter.
   g_autoptr(GPtrArray) locale_strings = g_ptr_array_new_with_free_func(g_free);
   for (int i = 0; languages[i] != nullptr; i++) {
-    gchar *language, *territory, *codeset, *modifier;
-    parse_locale(languages[i], &language, &territory, &codeset, &modifier);
+    gchar *language, *territory;
+    parse_locale(languages[i], &language, &territory, nullptr, nullptr);
     if (language != nullptr) {
       g_ptr_array_add(locale_strings, language);
     }
     if (territory != nullptr) {
       g_ptr_array_add(locale_strings, territory);
     }
-    if (codeset != nullptr) {
-      g_ptr_array_add(locale_strings, codeset);
-    }
-    if (modifier != nullptr) {
-      g_ptr_array_add(locale_strings, modifier);
-    }
 
     FlutterLocale* locale =
         static_cast<FlutterLocale*>(g_malloc0(sizeof(FlutterLocale)));
     g_ptr_array_add(locales_array, locale);
     locale->struct_size = sizeof(FlutterLocale);
     locale->language_code = language;
     locale->country_code = territory;
-    locale->script_code = codeset;
-    locale->variant_code = modifier;
+    locale->script_code = nullptr;
+    locale->variant_code = nullptr;
   }
   FlutterLocale** locales =
       reinterpret_cast<FlutterLocale**>(locales_array->pdata);