[Shipping Labels] Apply customs form automatically after pre-fill

[RafaelKayumov]

WOOMOB-734

Description

This is a follow PR to complete the recent customs data prefill feature: [Shipping Labels] Prefill customs form origin country.
The customs data became complete after a prefill without interacting with the customs form. But the customsForm instance wasn't assigned because the onCompletion callback was only triggered by a manual customs form dismissal.

In this PR we automatically trigger the assignment callback as soon as the customs form data becomes completed. And we do that just once to handle the customs data completion by just a pre-fill.

• Renamed onCompletion -> onFormReady since the callback is now not only related to the form editing completion.
• Listen to requiredInformationIsEntered and trigger onFormReady just once when data becomes completed.
• Updated tests

Testing steps

• Navigate to a completed order with an unfulfilled shipment with a foreign destination address.
• Go to "Create shipping label" flow
• Select the unfulfilled shipment
• Make sure the customs row is presented
• Make sure the customs row displays "Completed" status
• Don't open the customs form.
• Select a package and a rate
• Purchase label
• Make sure the purchase is completed without any errors. (It would fail if customs data is missing any required fields)
• Consider testing the flow with Proxyman. Track the /wcshipping/v1/label/purchase/[label id]&_method=post request and make sure the response contains proper customs data.

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	30940
	Version	PR #15853
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	5bc1a76
	Installation URL	2h6cphhm7o608

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[itsmeichigo]

I tested and confirmed the purchase success following the steps in the PR description.

However, I can still get a purchase failure if I edit the destination address from US to non-US (more details in a comment below).

I think it'd be simpler to add a computed variable for the customs form that can be retrieved from outside the view model. That way, we can avoid the complicated reactive code and closure. WDYT?

[itsmeichigo]

Just wondering: why is this necessary?

[RafaelKayumov]

I exposed it as read-only to be trackable in unit tests. Returned it back to be just private. Checking the customsForm from package instance instead.

[itsmeichigo]

Using first here can be risky. I still see the purchase failure with the following steps (edge case):

• Select an order with a US address as the destination.
• Edit the address to outside of the US.
• Proceed to purchase -> same error about missing customs form.