[ticket/12913] Add more parameters to core.submit_post_end event

As event core.modify_submit_post_data can modify any of the
function submit_post parameters, they may be needed to perform
actions directly after a post or topic has been submitted in
event core.submit_post_end (includes/functions_posting.php).

<a href="https://tracker.phpbb.com/browse/PHPBB3-12913">PHPBB3-12913</a>.