Consolidate merchant details before and after onboarding (5311)

[puntope]

Description

Use api.merchant.country instead of api.shop.country when applicable to select PayPal country when merchant is onboarded or shop country otherwise.

[github-actions]

Test using WordPress Playground

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What's included:

• ✅ WordPress (latest)
• ✅ WooCommerce (latest)
• ✅ PayPal Payments plugin v3.3.0-pr3890-19705881004-ge4bdb21 (built from this PR)

Login credentials:

• Username: admin
• Password: password

Plugin Details:

• Version: 3.3.0-pr3890-19705881004-ge4bdb21
• Commit: e4bdb21
• Artifact: woocommerce-paypal-payments-3.3.0-pr3890-19705881004-ge4bdb21

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_{🤖 Auto-generated for commit e4bdb21 • Last updated: 2025-11-26T13:55:30.124Z}