Just downloaded version 4.2 of SQL Developer. The formatter seems now to format the code better
xxcust_pkg.create_log_message( p_debug_level => lv_debug_level, p_procedure_name => lv_procedure_name, p_location_number => 10, p_message_string => NULL );
As Yan 1701 said, Oracle has improved the formatter in v4.2. But be aware that 4.2 is still in Early Adopter status. It's not a production-ready release yet.
You can also try version 4.1 to see if that helps. Your version is quite old.