topic action sheet: Align confirmation dialog text with web app

As suggested by Alya:
  https://chat.zulip.org/#narrow/stream/48-mobile/topic/confirm.2Fcancel.20modals/near/1401724

Author: chrisbobbe

src/action-sheets/index.js

@@ -269,8 +269,11 @@ const deleteTopic = {
   action: async ({ streamId, topic, dispatch, _ }) => {
     const confirmed = await new Promise((resolve, reject) => {
       Alert.alert(
-        _('Are you sure you want to delete the topic “{topic}”?', { topic }),
-        _('This will also delete all messages in the topic.'),
+        _('Delete topic', { topic }),
+        _(
+          'Deleting a topic will immediately remove it and its messages for everyone. Other users may find this confusing, especially if they had received an email or push notification related to the deleted messages.\n\nAre you sure you want to permanently delete “{topic}”?',
+          { topic },
+        ),
         [
           { text: _('Cancel'), onPress: () => resolve(false), style: 'cancel' },
           { text: _('Confirm'), onPress: () => resolve(true), style: 'destructive' },

static/translations/messages_en.json

@@ -119,8 +119,7 @@
   "Failed to unresolve topic": "Failed to unresolve topic",
   "No messages in topic: {streamAndTopic}": "No messages in topic: {streamAndTopic}",
   "Delete topic": "Delete topic",
-  "Are you sure you want to delete the topic “{topic}”?": "Are you sure you want to delete the topic “{topic}”?",
-  "This will also delete all messages in the topic.": "This will also delete all messages in the topic.",
+  "Deleting a topic will immediately remove it and its messages for everyone. Other users may find this confusing, especially if they had received an email or push notification related to the deleted messages.\n\nAre you sure you want to permanently delete “{topic}”?": "Deleting a topic will immediately remove it and its messages for everyone. Other users may find this confusing, especially if they had received an email or push notification related to the deleted messages.\n\nAre you sure you want to permanently delete “{topic}”?",
   "Unmute topic": "Unmute topic",
   "Mute stream": "Mute stream",
   "Unmute stream": "Unmute stream",