Implement ECE for payment processing on block checkout page

[Mayisha]

Fixes #3403 #3408

Changes proposed in this Pull Request:

• Created hooks, event-handlers and utils functions for ECE in blocks.
• The changes are made following the functions for payment-request and WooPayments.

Testing instructions

• Enable the ECE feature flag (return true from is_stripe_ece_enabled function or in your database add an option _wcstripe_feature_ece and set yes as the value).
• As a shopper add a product to your cart and go to the Block checkout page.
• Confirm that the Google Pay and Apple Pay buttons are loaded.
• Confirm that you can successfully place an order with Google Pay and Apple Pay.
• As a shopper add a product to your cart and go to the Block cart page.
• Confirm that the Google Pay and Apple Pay buttons are loaded.
• Confirm that you can successfully place an order with Google Pay and Apple Pay.
• Disable the feature flag and confirm that PRBs are still working without any regression.

[Mayisha]

@wjrosa I have requested your review as you are also working on ECE issues. Feel free to unassign yourself if you are too occupied 🍫

[Mayisha]

@wjrosa @annemirasol this PR is ready for review again. The changes seems to work for block cart page as well. So please test this on both the block cart and block checkout pages.

There are 2 issues I am going to fix separately.

• Empty space for Apple Pay container that @annemirasol mentioned in this comment. (Issue [ECE] Fix empty space for express checkout container #3470 )

• The payment method name is Credit/Debit Card instead of Google Pay or Apple Pay. This happens in the shortcode PR as well. So we will fix it later for both. (Issue [ECE] Fix payment method title for orders paid with ECE button  #3469)

[wjrosa]

Great work, Mayisha! Code is good and it works as expected:

Confirm that the Google Pay and Apple Pay buttons are loaded.

Confirm that you can successfully place an order with Google Pay and Apple Pay.

Confirm that the Google Pay and Apple Pay buttons are loaded.

Confirm that you can successfully place an order with Google Pay and Apple Pay.

Disable the feature flag and confirm that PRBs are still working without any regression.

[annemirasol]

This could be a me thing, but I can't get Apple Pay to show up on this branch, when ECE is enabled.

How it looks on develop, or for this branch when is_stripe_ece_enabled == false:

How it looks for this branch, with is_stripe_ece_enabled == true:

I was able to test Google Pay, and these scenarios worked as expected ✨

• Checkout: Google Pay displayed and working when is_stripe_ece_enabled is false
• Cart: Google Pay displayed and working when is_stripe_ece_enabled is false
• Checkout: Google Pay displayed and working when is_stripe_ece_enabled is true
• Cart: Google Pay displayed and working when is_stripe_ece_enabled is true

Some other things I observed, which I think are out-of-scope for this PR, but noting here to document. LMK if you want me to file issues for these.

• When Apple Pay/Google Pay are not enabled as payment methods, and is_stripe_ece_enabled istrue, I get empty boxes/sections.
• Noting that we may need to copy over the PRB fix for UAE addresses: Fix address fields mapping for Google Pay and UAE addresses #3432

Cart: Apple Pay/Google Pay are not enabled as payment methods, is_stripe_ece_enabled is true.

Checkout: Apple Pay/Google Pay are not enabled as payment methods, is_stripe_ece_enabled is true.

UAE addresses aren't being mapped correctly. This was recently fixed for PRBs:

[james-allan]

This could be a me thing, but I can't get Apple Pay to show up on this branch, when ECE is enabled.

Not just a you thing I thing. I'm seeing the same thing.

I noticed the following error in my console log:

Fixing that (see this comment) will fix it for me. :)

[Mayisha]

Thanks everyone for the review.

@annemirasol these are good findings.

When Apple Pay/Google Pay are not enabled as payment methods, and is_stripe_ece_enabled istrue, I get empty boxes/sections.

I will fix it under #3470

Noting that we may need to copy over the PRB fix for UAE addresses: #3432

I have fixed this in a1896eb and noted it in #3412