Core/Vehicles: - Redefine VEHICLE_SEAT_FLAG_USABLE as VEHICLE_SEAT_FLAG_CAN_ENTER_OR_EXIT. This flag determines whether or not the player has control over entering/exiting a vehicleseat. Thanks to linencloth for help with research.

- Implement VEHICLE_SEAT_FLAG_CAN_ENTER_OR_EXIT exit restriction
- Remove MOVEMENTFLAG_ROOT on vehicle exit

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

@@ -16435,7 +16435,7 @@ void Unit::ExitVehicle()
 
     SetControlled(false, UNIT_STAT_ROOT);
 
-    RemoveUnitMovementFlag(MOVEMENTFLAG_ONTRANSPORT);
+    RemoveUnitMovementFlag(MOVEMENTFLAG_ONTRANSPORT | MOVEMENTFLAG_ROOT);
     m_movementInfo.t_pos.Relocate(0, 0, 0, 0);
     m_movementInfo.t_time = 0;
     m_movementInfo.t_seat = 0;