feat(Core/Misc): change how Position struct is retrieved (#9017)

Update Position::GetPosition() and similar methods signatures to reflect 2a4c9bc changes by return a Position object instead of accepting a Position parameter by reference.

Cherry pick of https://github.com/TrinityCore/TrinityCore/commit/2585e799f95f259dd4b422daf15ef7963173c408

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

@@ -18833,7 +18833,7 @@ void Unit::_ExitVehicle(Position const* exitPosition)
 
     Position pos;
     if (!exitPosition)                          // Exit position not specified
-        vehicleBase->GetPosition(&pos);  // This should use passenger's current position, leaving it as it is now
+        pos = vehicleBase->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;