ECE: display notice on tax limitations

[annemirasol]

Changes proposed in this Pull Request:

Background
When taxes are based on billing address, we are unable to compute accurate taxes for express checkout. This is because we do not have access to the billing address until after the payment is submitted, i.e. we receive it only on the confirm event.

Currently, we are choosing to hide express checkout when:

• the product/cart is not shippable, e.g. virtual products
• taxes are based on billing address

In this PR, we add a notice pill for express checkout methods, to inform the merchant that even when enabled, Apple Pay, Google Pay, and Link will not be available if the above conditions are true.

Note: Amazon Pay is not included in these changes, as we will be turning it off outright when taxes are based on billing address. See STRIPE-377

Testing instructions

TBD

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• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Changelog entry

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Changelog Entry Comment

Comment

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[github-actions]

📈 PHP Unit Code Coverage Report

Package	Line Rate	Health
includes/admin/class-wc-stripe-settings-controller.php	20%	❌
Summary	44% (6949 / 15806)	❌