[Forwardport 2.3] allowed countries get countries for default scope

[swnsma]

Description

• fix 'if' for scope with id 0;
• add test for this case;
• Forwardport for PR 'Allowed Countries' - get countries for scope 'default'. #16693

Fixed Issues (if relevant)

1. magento/magento2#?: Not found relevant issue for the problem

Manual testing scenarios

Pre-conditions

1. Installation with website - Website and tore - Store.
2. Configured different 'Allowed Countries' for 'Default' and Store scopes.

Steps To Reproduce

1. Require Magento\Directory\Model\AllowedCountries class
2. Get Allowed Countries for default scope 0:
   Magento\Directory\Model\ResourceModel\Country::getAllowedCountries('ScopeInterface::SCOPE_STORE, 0)

Expected Result:

1. Returned Allowed Countries for Default config

Actual Result:

1. Will be returned Allowed Countries for default store - Store.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @swnsma. Thank you for your contribution
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[magento-engcom-team]

Hi @miguelbalparda, thank you for the review.
ENGCOM-2377 has been created to process this Pull Request

[magento-engcom-team]

Hi @swnsma. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.