Refactor all the “send_message” things.
Because it’s very messy. The passed arguments are very inconsistent, every-thing is different if it’s xmpp->irc or irc->xmpp, but they are confusingly called the same. We do the transforms (replace /me, cut between lines, etc) in a very inconsistent way, etc.
For example the “IrcClient::actual_send” callback should probably be just Bridge::send_xmpp_message_to_all_resources that already exists and is used for other normal messages received from IRC.
With this, fixing #3382 (closed) should be cleaner that “re-do the /me transform, in the opposite way, again, in a 4th different place in the code”.