[sim] Sim GUI DS: Add "Disconnected" state and start in it (#6218)

The default state for the DS in the simulated HAL is changed to disconnected.

The FMS view is now only editable in DS disconnected state.

This enables more robot and field-like testing of robot code, as the
alliance color and other parameters start in invalid states and are
only set when the DS connects.

hal/src/main/native/sim/DriverStation.cpp

@@ -382,6 +382,7 @@ void NewDriverStationData() {
   }
   lastGiven = given;
 
+  SimDriverStationData->dsAttached = true;
   driverStation->newDataEvents.Wakeup();
   SimDriverStationData->CallNewDataCallbacks();
 }