l10n: Add stub translation for nb (Norwegian Bokmål).

This is represented in Weblate as `app_nb_NO.arb`, which is not
supported without the existence of a bare `app_nb.arb`.  Adding a
bare `app_nb.arb` for now may allow Weblate's aliases[^1] to map the
`nb_NO` to a file name `app_nb.arb`.

[^1]: https://docs.weblate.org/en/latest/admin/projects.html#project-language-aliases

Author: alexmv

assets/l10n/app_nb.arb

@@ -0,0 +1 @@
+{}

lib/generated/l10n/zulip_localizations.dart

@@ -9,6 +9,7 @@ import 'zulip_localizations_ar.dart';
 import 'zulip_localizations_en.dart';
 import 'zulip_localizations_fr.dart';
 import 'zulip_localizations_ja.dart';
+import 'zulip_localizations_nb.dart';
 import 'zulip_localizations_pl.dart';
 import 'zulip_localizations_ru.dart';
 
@@ -99,6 +100,7 @@ abstract class ZulipLocalizations {
     Locale('ar'),
     Locale('fr'),
     Locale('ja'),
+    Locale('nb'),
     Locale('pl'),
     Locale('ru')
   ];
@@ -1025,7 +1027,7 @@ class _ZulipLocalizationsDelegate extends LocalizationsDelegate<ZulipLocalizatio
   }
 
   @override
-  bool isSupported(Locale locale) => <String>['ar', 'en', 'fr', 'ja', 'pl', 'ru'].contains(locale.languageCode);
+  bool isSupported(Locale locale) => <String>['ar', 'en', 'fr', 'ja', 'nb', 'pl', 'ru'].contains(locale.languageCode);
 
   @override
   bool shouldReload(_ZulipLocalizationsDelegate old) => false;
@@ -1040,6 +1042,7 @@ ZulipLocalizations lookupZulipLocalizations(Locale locale) {
     case 'en': return ZulipLocalizationsEn();
     case 'fr': return ZulipLocalizationsFr();
     case 'ja': return ZulipLocalizationsJa();
+    case 'nb': return ZulipLocalizationsNb();
     case 'pl': return ZulipLocalizationsPl();
     case 'ru': return ZulipLocalizationsRu();
   }