[ECE] Spike: Investigate missing parities between ECE and PRB.

[Mayisha]

All the basic features for ECE has been added to the epic.

This spike is to investigate and find out if there are any more features and compatibilities available in PRB and missing in the ECE implementation.

[Mayisha]

Found two missing fixes we need to bring over from PRBs.

• Fix required fields breaking Google Pay and Apple pay (Fix required fields breaking Google Pay and Apple pay #2886)
  • Addressed in Implement ECE for payment processing on block checkout page #3439
• Fix address fields mapping for Google Pay and UAE addresses (Fix address fields mapping for Google Pay and UAE addresses #3432)
  • Addressed in Implement ECE for payment processing on block checkout page #3439

[Mayisha]

I have tested different scenarios of express payment with PRB and ECE in order to make the comparison and figure out any missing parities.
Additionally, I have gone through the WooPayments GH repository to investigate the issues related to the ECE project. I have summarized the issues here( 1s10sYxTgQMIC2FsosuFwf_4VtdJU57ErrEznkLA5rVM-gdoc ) along with the status of them in the Stripe plugin.

Worked on the following PRs as part of the follow up of this investigation.

• Fix Stripe disable modal text #3526
• Add logging in Ajax requests for ECE #3533
• Miscellaneous tasks on ECE #3551
• Do not load ECE button if total amount is 0 #3553
• Show ECE button in settings preview #3579