message send: Refactor how user data is sent for the event.

This is a prep change for calling `get_active_presence_idle_user_ids`
after we have collected all user data variables, so that that function
does not erroneously skip some user IDs from not having the complete
data.

zerver/lib/actions.py

@@ -1973,14 +1973,13 @@ def do_send_messages(
         else:
             user_list = list(user_ids)
 
-        users: List[Dict[str, Union[int, List[str], bool]]] = []
+        user_data_objects: List[UserMessageNotificationsData] = []
         for user_id in user_list:
             flags = user_flags.get(user_id, [])
             wildcard_mention_notify = (
                 user_id in send_request.wildcard_mention_user_ids and "wildcard_mentioned" in flags
             )
-            users.append(
-                asdict(
+            user_data_objects.append(
                 UserMessageNotificationsData(
                     id=user_id,
                     flags=flags,
@@ -1992,7 +1991,8 @@ def do_send_messages(
                     sender_is_muted=(user_id in send_request.muted_sender_user_ids),
                 )
             )
-            )
+
+        users = [asdict(user_data_object) for user_data_object in user_data_objects]
 
         if send_request.message.is_stream_message():
             # Note: This is where authorization for single-stream