Test cases:
1. Target is not threatened.
The IP should be placed on a direct heading from the origin to the
target at the max ingress distance, or very near the origin airfield
if the airfield is closer to the target than the IP distance.
2. Unthreatened home zone, max IP between origin and target, safe
locations available for IP.
The IP should be placed in LAR at the closest point to home.
3. Unthreatened home zone, origin within LAR, safe locations available
for IP.
The IP should be placed near the origin airfield to prevent
backtracking more than needed.
4. Unthreatened home zone, origin entirely nearer the target than LAR,
safe locations available for IP.
The IP should be placed in LAR as close as possible to the origin.
5. Threatened home zone, safe locations available for IP.
The IP should be placed in LAR as close as possible to the origin.
6. No safe IP.
The IP should be placed in LAR at the point nearest the threat
boundary.
This is a pretty janky system until we get add context menu support. For
now the destination is set by dragging the CV marker and cleared by
right clicking the destination marker. Once we have a context menu a
context action will begin setting the destination the way it did in the
old UI, and the destination marker will be draggable.
These are an implementation quirk, and passing them to the UI just means
that we put TGO pins on top of the CP, which makes the base menu
unopenable.
In the old UI we avoided this by not drawing anything that was
`for_airbase`, but now that we can zoom in further we're drawing base
defenses.
https://bugreports.qt.io/browse/PYSIDE-1426
For whatever reason this only shows up in packaged builds for us, and
also the recommended workaround of using a member property rather than a
decorated method does not work for us.
Until PySide2 5.15.3 (or later) is released, we need to use a named
signal for every property we expose.
