This appears to be incompatible with pyinstaller. I get the following
when trying to run the executable generated with pyside6:
```
Traceback (most recent call last):
File "qt_ui\main.py", line 29, in <module>
File "PyInstaller\loader\pyimod03_importers.py", line 476, in exec_module
File "qt_ui\windows\QLiberationWindow.py", line 28, in <module>
File "PyInstaller\loader\pyimod03_importers.py", line 476, in exec_module
File "qt_ui\widgets\map\QLiberationMap.py", line 11, in <module>
ImportError: could not import module 'PySide6.QtPrintSupport'
```
Doesn't allow helos or harriers to do it either even though they should
be able to because we don't currently support ground spawns, which would
be needed to prevent those aircraft from using the runway. Even then, I
don't know if they can be forced to *land* vertically.
Fixes https://github.com/Khopa/dcs_liberation/issues/432
Breaks save compat because it adds new fields to `Flight` that have no
constant default. Removing all of our other save compat at the same
time.
Note that player flights with a divert point will have a nav point for
their actual landing point. This is because we place the divert point
last, and DCS won't let us have a land point anywhere but the final
waypoint. It would allow a LandingReFuAr point, but they're only
generated for player flights anyway so it doesn't really matter.
Fixes https://github.com/Khopa/dcs_liberation/issues/342
