notif [nfc]: Use localization for self user display name

Author: rajveermalviya

assets/l10n/app_en.arb

@@ -479,5 +479,9 @@
       "senderFullName": {"type": "String", "example": "Alice"},
       "numOthers": {"type": "int", "example": "4"}
     }
+  },
+  "notifSelfUser": "You",
+  "@notifSelfUser": {
+    "description": "Display name supposed to be temporarily displayed after replying to a message in Android notification"
   }
 }

lib/notifications/display.dart

@@ -108,7 +108,7 @@ class NotificationDisplayManager {
       messagingStyle = MessagingStyle(
         user: Person(
           key: _personKey(data.realmUri, data.userId),
-          name: 'You'), // TODO(i18n)
+          name: zulipLocalizations.notifSelfUser),
         messages: [],
         isGroupConversation: switch (data.recipient) {
           FcmMessageStreamRecipient() => true,

test/notifications/display_test.dart

@@ -10,6 +10,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:zulip/api/model/model.dart';
 import 'package:zulip/api/notifications.dart';
 import 'package:zulip/host/android_notifications.dart';
+import 'package:zulip/model/localizations.dart';
 import 'package:zulip/model/narrow.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/notifications/display.dart';
@@ -75,6 +76,7 @@ MessageFcmMessage messageFcmMessage(
 
 void main() {
   TestZulipBinding.ensureInitialized();
+  final zulipLocalizations = GlobalLocalizations.zulipLocalizations;
 
   Future<void> init() async {
     addTearDown(testBinding.reset);
@@ -149,7 +151,7 @@ void main() {
               ..user.which((it) => it.isNotNull()
                 ..iconBitmap.isNull()
                 ..key.equals(expectedSelfUserKey)
-                ..name.equals('You')) // TODO(i18n)
+                ..name.equals(zulipLocalizations.notifSelfUser))
               ..isGroupConversation.equals(expectedGroup)
               ..conversationTitle.equals(expectedTitle)
               ..messages.which((it) => it