CRF 47919: Shopping Cart: Item quantity can exceed 999

Problem:  There is no validation to check if PreCartLineItem and ShoppingCartLineItem exceeds 999. this bug allows the user to purchase insane quantities for certain items.

Solution: add validation to compute the quantity for both PreCartLineItem (the items that the user wants to add to cart) and ShoppingCartLineItem (the items that are already in cart). Ensure that the quantity does not exceed 999