[Forwardport] Improve "Invalid country code" error message on tax import

[ihor-sviziev]

Original Pull Request

#16873

Description

This change helps when importing tax CSVs by telling the user which country is responsible for the error being thrown. Without this it is a very annoying error to get and the user just has to guess.

Before:

After:

Manual testing scenarios

Create a tax import CSV with an inavlid country code, for example:

Code	Country	State	Zip/Post Code	Rate	Zip/Post is Range	Range From	Range To
Puerto Rico	PR	*	*	20

Then attempt to import the CSV by going to Magento Admin > System > Data Transfer > Import/Export Tax Rates

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 @ihor-sviziev. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @ihor-sviziev. 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.