[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/12025] Post Preview no longer shows warnings

https://tracker.phpbb.com/browse/PHPBB3-12025

PHPBB3-12025
[ticket/12025] Don't show any error on preview if the message is empty

PHPBB3-12025
[ticket/12025] Fixing the condition....

PHPBB3-12025
[ticket/12431] Add has_poll icon to topiclists

PHPBB3-12431
[ticket/12451] Split TOO_FEW_CHARS_LIMIT for plurals

PHPBB3-12451
[ticket/12451] Split TOO_MANY_CHARS vars for plurals

PHPBB3-12451
[ticket/12451] Use new line to concatenate strings

PHPBB3-12451
[ticket/12451] Remove duplicated lang var

PHPBB3-12451
[ticket/12431] Add topic poll icon.

PHPBB3-12431
Merge pull request #4 from prototech/ticket/12431

[ticket/12431] Add topic poll icon.
[ticket/12325] Generate the list of the deleted files and folders

https://tracker.phpbb.com/browse/PHPBB3-12325

PHPBB3-12325
[ticket/12325] Add files located in deleted dirs

PHPBB3-12325
[ticket/12325] Add visibilities

PHPBB3-12325
[ticket/12325] Change private function to protected

PHPBB3-12325
[ticket/12025] Apply DeMorgan

PHPBB3-12025