[Backport] Make it possible to generate sales PDF's using the API

[amol2jcommerce]

Original Pull Request

#20043

Description (*)

Currently if you try to generate an invoice PDF using a custom API endpoint, you will get the exception: Invalid template file: 'Magento_Payment::info/pdf/default.phtml' because you are not in the adminhtml scope or the frontend scope which is the only place where this template lives.

Because app/code/Magento/Payment/view/adminhtml/templates/info/pdf/default.phtml === app/code/Magento/Payment/view/frontend/templates/info/pdf/default.phtml it is safe to move that file to app/code/Magento/Payment/view/base/templates/info/pdf/default.phtml. I'll leave the adminhtml and frontend templates in place for backward compatibility.

Fixed Issues (if relevant)

1. none

Manual testing scenarios (*)

1. Create an API endpoint which generates an invoice PDF
2. Calling that endpoint should not result in an error

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 @amol2jcommerce. Thank you for your contribution
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[magento-engcom-team]

Hi @rogyar, thank you for the review.
ENGCOM-4368 has been created to process this Pull Request

[VasylShvorak]

✔️ QA passed

[ghost]

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