[ECE] Implement ECE for payment processing on shortcode cart page

[Mayisha]

Description

Display the ECE button and process payment with the button on the shortcode cart page.

Acceptance Criteria

• ECE buttons are rendered on the shortcode cart page.
• You can successfully process payment with the ECE button from the shortcode cart page.
• Both success and failure cases are handled including necessary notices.

[james-allan]

Just noting that the cart integration is the same as the checkout integration being built in https://github.com/woocommerce/woocommerce-gateway-stripe/pull/3436. I'm going to leave this one for now and wait until that PR is merged.

Blocked by: https://github.com/woocommerce/woocommerce-gateway-stripe/pull/3436

[james-allan]

https://github.com/woocommerce/woocommerce-gateway-stripe/pull/3436 has been merged now so I'm unblocking this.

I think this issue will need to take an approach of did the work in #3436 also implement it for the shortcode cart page.