Resending the confirmation email is rendered with default template

Problem/Motivation

An order confirmation email is rendered with the template shipping with commerce core if the email is resend using the respective button in the backend.

Steps to reproduce

1. Setup commerce, postoffice, postoffice commerce, a custom theme, customize postoffice-commerce-email.html.twig
2. Create a new order, capture order receipt email, observe that the custom template was used.
3. Navigate to the order in the commerce core backend and resend the confirm email.
4. Capture order receipt email and observe that the default template was used.

Proposed resolution

Introduce an OrderReceiptEmail class with a buildThemedEmail() method which builds the commerce_order_receipt render array from scratch.

Remaining tasks

User interface changes

API changes

Data model changes