Extract data handling classes to extension sdk

INFO

This document represents an architecture decision record (ADR) and has been mirrored from the ADR section in our Shopware 6 repository. You can find the original version here

Context

• The package @shopware-ag/meteor-extension-sdk will be referred to as sdk
• The ts/js implementation of the Administration is referred to as administration

Previously the administration held the implementation of the classes Entity, EntityCollection and Criteria. This led to the problem, that the sdk was unable to identify instances of these classes easily. Since the administration is not a standalone package that could be imported in the sdk. Also, the sdk would need to copy the implementation since we want to copy the administration data handling in the sdk.

Decision

Move the implementation of Entity, EntityCollection and Criteria to the sdk. The corresponding files in the administration simply forward the default export of the sdk.

Consequences

This will result in the same behaviour for current implementations. On the other hand, it provides the benefit of having these basic classes in an external package anybody can use.