refactor calculate_invite_state

That was terribly named and terribly implemented.

Co-authored-by: Charles Hall <charles@computer.surgery>

src/api/client_server/membership.rs

@@ -1307,7 +1307,7 @@ pub(crate) async fn invite_helper(
                 )?;
 
             let invite_room_state =
-                services().rooms.state.calculate_invite_state(&pdu)?;
+                services().rooms.state.get_helpful_invite_events(&pdu)?;
 
             drop(room_token);