minor: Clean up args for apply_event.

We now require keywords, so that there is no
pitfall for mixing up boolean parameters.
Positional parameters are basically evil
when you have a bunch of bools.

I also make user_profile the first argument.

Finally, the code is more diff-friendly.

docs/tutorials/new-feature-tutorial.md

@@ -359,7 +359,10 @@ race conditions.
         state['realm_allow_message_editing'] = user_profile.realm.allow_message_editing
         # ...
 
-    def apply_event(state, events, user_profile, include_subscribers):
+    def apply_event
+        user_profile: UserProfile,
+        # ...
+    ) -> None:
       for event in events:
         # ...
         elif event['type'] == 'realm':