Currently, when users open a DMN 1.1 or a DMN 1.3 model, the marshaller just fails, and users see the XML editor.

This aims to cover the DMN 1.1 and DMN 1.3 pre-convertion mechanism. So, users will be able to open DMN 1.1 and DMN 1.3 models [1] in the DMN editor, but continue opening/saving them as DMN 1.2 model. Thus, it's not the goal of this epic too support the DMN 1.3 spec, the BAPL-1489 will cover the DMN 1.3 spec support.

Acceptance criteria:

• As a user, I want to open a DMN 1.1 model in the DMN editor without failure, and save it as a DMN 1.2 model
• As a user, I want to open a DMN 1.3 model in the DMN editor without failure, and save it as a DMN 1.2 model

Supported features

• Any DMN 1.1/1.3 model with nodes and connectors must be successfully opened as a DMN 1.2 model
• Any DMN 1.1/1.3 model with data types must be successfully opened as a DMN 1.2 model
• Any DMN 1.1/1.3 model with a decision node with a valid boxed expression [2] must be successfully opened as a DMN 1.2 model
• Any DMN 1.1/1.3 model with a valid boxed expression must be successfully opened as a DMN 1.2 model

[1] Users will be able to open DMN 1.3 that do not use DMN 1.3 features (main DMN 1.3 features: "Groups" - a visual mechanism to group elements of a diagram informally; and "Function Data Types" - https://www.omg.org/spec/DMN/1.3/PDF/changebar).
[2] Literal expressions, Contexts, Decision Tables, Relations, Functions, Invocations, Lists