update-message: Use MentionData in the update_message_backend code.

This is a performance optimization, since we can avoid doing work
related to wildcard mentions in the common case that the message can't
have any.  We also add a unit test for adding wildcard mentions in a
message edit.

zerver/lib/actions.py

@@ -4436,7 +4436,7 @@ def do_update_embedded_data(user_profile: UserProfile,
 def do_update_message(user_profile: UserProfile, message: Message, topic_name: Optional[str],
                       propagate_mode: str, content: Optional[str],
                       rendered_content: Optional[str], prior_mention_user_ids: Set[int],
-                      mention_user_ids: Set[int]) -> int:
+                      mention_user_ids: Set[int], mention_data: Optional[bugdown.MentionData]=None) -> int:
     """
     The main function for message editing.  A message edit event can
     modify:
@@ -4471,6 +4471,9 @@ def do_update_message(user_profile: UserProfile, message: Message, topic_name: O
         assert rendered_content is not None
         update_user_message_flags(message, ums)
 
+        # mention_data is required if there's a content edit.
+        assert mention_data is not None
+
         # One could imagine checking realm.allow_edit_history here and
         # modifying the events based on that setting, but doing so
         # doesn't really make sense.  We need to send the edit event
@@ -4513,7 +4516,7 @@ def do_update_message(user_profile: UserProfile, message: Message, topic_name: O
             recipient=message.recipient,
             sender_id=message.sender_id,
             stream_topic=stream_topic,
-            possible_wildcard_mention=True,
+            possible_wildcard_mention=mention_data.message_has_wildcards(),
         )
 
         event['push_notify_user_ids'] = list(info['push_notify_user_ids'])