Add state code mapping for Ukraine regions

[diegocurbelo]

Fixes STRIPE-726
Fixes #4691

Changes proposed in this Pull Request:

This PR extends the current state mapping to add the mappings for the Ukrainian regions (ex: Kyiv -> UA-30).

Testing instructions

Copied from the issue report

1. Enable Stripe Payment Request buttons (Google Pay).
2. Set the store country to Slovenia, and allow selling to all countries.
3. Try to pay with a Ukrainian card via Google Pay.
4. Verify that the checkout succeeds.

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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)

[Copilot]

Pull Request Overview

This PR adds state code mappings for Ukrainian regions to support Stripe payment request buttons. The implementation maps Ukrainian regional names (in English and Ukrainian) to their corresponding ISO 3166-2 subdivision codes.

• Adds complete mapping for all Ukrainian oblasts and cities with their ISO codes
• Updates changelog entries to document the fix

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
includes/constants/class-wc-stripe-payment-request-button-states.php	Adds comprehensive Ukrainian state mapping with regional codes and names in multiple languages
readme.txt	Documents the Ukraine state mapping fix in the changelog
changelog.txt	Documents the Ukraine state mapping fix in the changelog

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