Added field to Cart representing the total quantity of all Line Items

We added the totalLineItemQuantity field to Cart that represents the sum of all Line Item quantities. Its value does not take the Cart's Custom Line Items into consideration. With this, there is no need for you any more to calculate this value on the client side.

Changes:

• [API] Added totalLineItemQuantity field to Cart.
• [GraphQL API] Changed the Cart type:
  • Added the totalLineItemQuantity field to the Cart type.

The following changes were introduced in terms of GraphQL SDL:

extend type Cart {
  totalLineItemQuantity: Long
}