Some code refactoring to allow mission titles to be strings of any length. Titles that are too long to actually display (based on string width) will be visibly truncated using `font::force_fit_string`, but the underlying title will not be affected. Multiplayer is still subject to the 31-character length limit, so titles sent over the network will still have characters truncated.
Also removes some redundant calls to `gr_get_string_size`, since `font::force_fit_string` returns the fitted string width.
This was needed by the restart dialog action and got removed since the
Discord changes needed to know if a mission was active or not.
I removed the code which changed the mission file name and replaced it
with some internal handling in the discord code which should now handle
mission restarts better.
This fixes#1815.
This uses the Discord Rich Presence API for improving the integration of
FSO into Discord. At the moment this includes state notifications for
being in the main hall, the command and mission briefing and in-mission.
When in-mission it also includes the elapsed time of the mission with
support for time compression.
The details part of the notification includes the campaign name and
mission name if possible.
Goober5000