Separate cart items are created instead of quantity increment

[TomashKhamlai]

... and update of the last cart-items discards an update that was applied to the first cart-item. Cart-items are never joined together.

Related to #699

The cart is not updating properly: new cart items are created instead of changing quantity while adding the same product to the cart. At the same time update of the first cart-item do not trigger recalculation while update of the last one joins them back together.

Note: could be specific to customizable_options

c7d9130

Preconditions (*)

1. Create a configurable product with a customizable option that is not required
   

2. Add this product to cart via addConfigurableProductsToCart. Specify that package is D and quantity is 1

3. Change quantity to 2 via updateCartItems

4. Add this product to cart via addConfigurableProductsToCart. Specify that package is D and quantity is 3 (repeat what was done in step 2 without any changes. Even quantity is updated it is still the same cartItem)

5. Verify that your cart contains 2 cart items. Stop reproducing here if your information differs. For example:

{
  "data": {
    "updateCartItems": {
      "cart": {
        "items": [
          {
            "id": "27",
            "quantity": 1
          },
          {
            "id": "29",
            "quantity": 3
          }
        ]
      }
    }
  }
}

Steps to reproduce (*)

1. Update the first item

mutation {
  updateCartItems(input: {
    cart_id: "X9klnJz5K840LhG22VeJPvoOnHFZ6KsZ"
    cart_items: {
      cart_item_id: 27
      quantity: 4
      
    }
  }) {
    cart {
      items {
        id
        quantity
      }
    }
  }
}

My result was:

{
  "data": {
    "updateCartItems": {
      "cart": {
        "items": [
          {
            "id": "27",
            "quantity": 4
          },
          {
            "id": "29",
            "quantity": 3
          }
        ]
      }
    }
  }
}

2. Update last item

mutation {
  updateCartItems(input: {
    cart_id: "X9klnJz5K840LhG22VeJPvoOnHFZ6KsZ"
    cart_items: {
      cart_item_id: 29
      quantity: 4
      
    }
  }) {
    cart {
      items {
        id
        quantity
      }
    }
  }
}

Expected result (*)

1. Predictive behavior
2. Quantity increment for the request with the same product
3. Changes to one item do not have an impact on another item

Actual result (*)

{
  "data": {
    "updateCartItems": {
      "cart": {
        "items": [
          {
            "id": "27",
            "quantity": 1
          },
          {
            "id": "29",
            "quantity": 4
          }
        ]
      }
    }
  }
}

[Rus0]

Duplicate of #792