Changes to Cart token format for AJAX and Storefront GraphQL Cart APIs

Cart tokens will now be returned with a new format for both the AJAX and Storefront GraphQL Cart APIs. API features and functionality remain unchanged. Apps and themes should be designed to handle cart tokens in any format and of any length. Treat the cart token as a random identifier that will change in the future.

Action Required: Ensure that any app and theme code is free from hard-coded assumptions (ex. Using regex to identify a cart token) on the format and structure of the cart token.