Core/Misc: Change how Position struct is retrieved

Update Position::GetPosition() and similar methods signatures to reflect 2a4c9bcaf9 changes by return a Position object instead of accepting a Position parameter by reference.

src/server/game/Entities/Unit/Unit.cpp

@@ -16907,7 +16907,7 @@ void Unit::_ExitVehicle(Position const* exitPosition)
 
     Position pos;
     if (!exitPosition)                          // Exit position not specified
-        vehicle->GetBase()->GetPosition(&pos);  // This should use passenger's current position, leaving it as it is now
+        pos = vehicle->GetBase()->GetPosition();  // This should use passenger's current position, leaving it as it is now
                                                 // because we calculate positions incorrect (sometimes under map)
     else
         pos = *exitPosition;