[ticket/12407] Allow changing of post_data, etc. at end of posting.php

The current event core.posting_modify_template_vars is just ran using dispatch
but it doesn't pass any data from posting.php to the listener. Because of that,
it's not possible to know anything from posting.php and therefore limits the
use cases of this event. This will change it to allow similar actions as with
the event core.modify_posting_parameters.

PHPBB3-12407
[ticket/12407] Add message_parser as passed variable to event

PHPBB3-12407
Merge branch 'develop-ascraeus' of https://github.com/phpbb/phpbb into ticket/12407

Conflicts:
	phpBB/posting.php
[ticket/12407] Assign template variables again after merging develop-ascraeus

PHPBB3-12407
[ticket/12407] Merge @change in doc block of event

PHPBB3-12407
[ticket/10737] Adding username suggestions in "Find a member" using AJAX

PHPBB3-10737
[ticket/10737] Improvements over last commit

PHPBB3-10737
[ticket/10737] Code fixes in AJAX search feature

PHPBB3-10737
[ticket/10737] Using JQuery events and JSON response.

PHPBB3-10737
[ticket/10737] Removing unnecessary/obsolete code.

PHPBB3-10737
[ticket/10737] Avoid hard-coding table row and use case-insensitive search.

PHPBB3-10737
[ticket/10737] Removing obsolete code.

PHPBB3-10737
[ticket/10737] Using UTF-8 aware alternatives in PHP code.

PHPBB3-10737
[ticket/10737] Adding delayed keyup and removing target_blank.

PHPBB3-10737
[ticket/10737] Use dropdown for search results container.

PHPBB3-10737
[ticket/10737] Clean up memberlist.php.

PHPBB3-10737
[ticket/10737] Add a more generic live search implementation.

PHPBB3-10737
[ticket/10737] Drop subsilver2 changes.

PHPBB3-10737
[ticket/10737] Set the username as the input value instead of redirecting.

PHPBB3-10737
[ticket/10737] Load core.js and ajax.js in simple_footer.html.

PHPBB3-10737