Implement Tokenized Cart Enhancements in ECE Implementation

[frosso]

Integrate bug fixes and improvements from the Tokenized Cart PRB, including order attribution, booking compatibility, currency handling, and cart management on product pages. This will ensure the unified codebase incorporates the benefits of both implementations

For background: pbIwZe-2ur-p2

Acceptance criteria

• The new copy is integrated with the Store API rather than the current AJAX endpoints.
• ECE JavaScript implementation is duplicated and updated to include the following Tokenized Cart fixes:
  • Order attribution for logged-in users.
  • Compatibility support for local pickup from WooCommerce Store API/WooCommerce Blocks
  • Compatibility with bookings and correct order summary amounts.
  • Proper handling of zero-decimal currencies.
  • Display accuracy for products with special characters.
  • Compatibility with plugins affecting shipping rates and fees.
  • Retention of main cart contents on product page purchases.
  • Custom WooCommerce Session Handler is retained to manage the cart effectively.
• The copied implementation is accessible behind the _wcpay_feature_tokenized_cart_ece feature flag
• Block-based cart & checkout, shortcode-based cart & checkout, pay-for-order page, product page are all functional and using the tokenized cart ECE implementation

[frosso]

It wasn't completed, we're still missing product page implementation & ensuring the previous tokenized-cart enhancements are still viable :)