updateCartItem method
Update cart item quantity.
Updates the quantity of a specific item in the shopping cart.
itemId
the ID of the cart item to update
quantity
the new quantity (0 will remove the item)
Returns true
if quantity was updated successfully, false
otherwise.
Implementation
Future<bool> updateCartItem(String itemId, int quantity) {
throw UnimplementedError('updateCartItem() has not been implemented.');
}