Epic: Migrate Stripe PRB to ECE

[bborman22]

The goal of this project is to migrate from Stripe's PaymentRequestButton to Stripe's ExpressCheckoutElement for express checkout buttons in WooPayments.

In doing this migration we aim to increase the number of express payment and wallet options available in WooPayments. We also will aim to address as many existing issues with PRB today as we can using the new tools available with ECE. The project will be considered complete once all express checkout options are using ECE and we've cleaned up the unused PRB code.

Reading Materials
Early exploration into ECE: pbIwZe-1QB-p2
Description of some of the problems we're facing with PRB: paJDYF-ckK-p2
Early Layout of Phases: #8501

Milestones

Milestone 1

Beta Give feedback

1. Render the payment buttons using ECE behind a feature flag. #8772
   focus: checkout payments +1
   
2. Integrate ECE for Payment Processing in the Blocks Checkout Page #8773
   focus: checkout payments +1
   
3. Refactor codebase to decouple PRB utils dependencies #8825
   focus: checkout payments +1
   

Milestone 2

Beta Give feedback

1. Integrate ECE for Payment Processing in the Blocks Cart Page #8867
   focus: checkout payments +1
   
2. Integrate ECE for Payment Processing in the product page #8868
   focus: checkout payments +1
   
3. Integrate ECE for Payment Processing in the Shortcode Cart/Checkout #8870
   focus: checkout payments +1
   
4. Integrate ECE Payment Processing for the Pay for Order Endpoint #8869
   focus: checkout payments +1
   
5. Ensure ECE Implementation Supports the Same Plugins and Product Types as PRBs #8871
   focus: checkout payments +1
6. Ensure Compatibility with the Cart Tokenization Project #8947
   focus: checkout payments +1
7. Spike: Investigate if changes are needed to support Apple Pay in ECE #8873
   focus: checkout payments +1
   
8. Spike: investigate compatibility between Link and WooPay when Link is offered in ECE #8874
   focus: checkout payments +1
9. Spike: investigate if ECE payment methods can be registered individually #8872
   focus: checkout payments +1

Milestone 3

Beta Give feedback

1. Ensure Button Settings are applied in ECE and Obtain Design Approval #8951
   0 of 3
   focus: checkout payments needs design +2

Milestone 4

Beta Give feedback

1. Ensure the Telemetry events for PRBs are Implemented into ECE #8948
   focus: checkout payments +1

Milestone 5

Beta Give feedback

1. Set ECE as Default for Express Checkout Buttons #8949
   focus: checkout payments +1

Milestone 6

Beta Give feedback

1. Remove ECE feature flag and clean-up PRB code #8950
   0 of 3
   focus: checkout payments +1

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