Putting the ingress point directly on one end of the FLOT means that AI
flights won't start searching and engaging targets until they reach that
point. If the front line has advanced toward the flight's departure
airfield, it might overfly targets on its way to the IP.
Instead, place an IP for CAS the same way we place any other IP. The AI
will fly to that and start searching from there.
This also:
* Removes the midpoint waypoint, since it didn't serve any real purpose
* Names the FLOT boundary waypoints for what they actually are
Fixes https://github.com/dcs-liberation/dcs_liberation/issues/2231.
mypy struggles to prove this cast correct when there are two or'd
isinstance checks where both types coincidentally have properties of the
same name (but no defined protocol making that explicit). I'm not really
sure why mypy is happy with this in its current state, but it isn't
after a change I'm making.
All our isinstance use is a bit of an anti-pattern anyway, so extract a
method that exposes the data we care about.
The start/end times for tankers aren't actually used, so this could be
simplified even more, but that data _should_ be used.
