Fix sending the correct pressure altitude for a pilot position

* Before this commit, only the true altitude was known for an aircraft situation. The pressure altitude was not available anywhere yet.
* This caused a wrong altitude in radar clients.
* We fix this reading the pressure altitude from the simulators and set it in the own aircraft situation.
* MS Flight Simulators have the pressure altitude in the APIs available.
* For X-Plane and emulated simulator, we need to calculate it from the pressure at sea level.
* Finally, we use the new available pressure altitude to send it to the FSD server.

Maniphest Tasks: Ref T223

src/plugins/simulator/fs9/simulatorfs9.cpp

@@ -397,6 +397,7 @@ namespace BlackSimPlugin
                 simDataOwnAircraft.getCom2System(),
                 simDataOwnAircraft.getTransponder(),
                 this->identifier());
+            this->updateOwnSituation(simDataOwnAircraft.getSituation());
             reverseLookupAndUpdateOwnAircraftModel(simDataOwnAircraft.getModelString());
         }