Improve Import Resolver logic

[yesamer]

Follow-up of https://github.com/apache/incubator-kie-issues/issues/1150.

After the analysis of that part of the code, several improvements should be applied:

• An old custom drools:modelName attribute is used in the logic. That attribute is a custom definition (i.e. not present in the DMN specs) no longer used in our implementation since DMN 1.1 version. Considering that the XSD that defines that attribute is no longer present in our codebase, the only reference of that attribute is present in the 1.1 TImport class, and our editors are not managing it at all, we agreed to remove any reference to that attribute in the logic
• The new logic, should rely on the namespace only to resolve the imported DMN file. The namespace of the Definition metamodel doesn't ensure this attribute is unique over all DMNs of the entire project, so a collision may happen. In addition, the Import metamodel paragraph says: The namespace value should be globally unique, which in our interpretation doesn't force all the namespace to be unique but the required conditions to have a correct import resolution, without saying how to manage a possible collision. In case of collisions (i.e. multiple DMN files with the same namespace in the Definition metamodel), the idea is to rely on the locationURI attribute to correctly resolve the DMN model to be imported. The locationURI is optional, so the logic should manage such a scenario as well.
• DMNResource and DMNModel DTOs have a very similar scope and fields. It seems the first one holds DMN files not yet compilated, while the latter is managing the already compilated ones. It could be possible to unify those DTOs - TBA
• The overall logic that resolves and compiles the DMN assets and their dependencies with their Imported DMN could be improved. Multiple call to the Import resolver could be avoided. Some dmnModels are added from a source that seems no longer used (business-central) TBA

@gitgabrio

[jomarko]

What is the effect on the UI Side on the tooling @yesamer please? Do we need to remove/add some UI field in the popover for the importing model? Or should we remove some field form the UI Cards for displaying existing imports?

[gitgabrio]

@jomarko @tiagobento @yesamer This is something that will be implemented during server-side validation. It is up to tooling-team to decide if some preventive check should be made directly in UI, e.g. when a folder/project is imported, or when an import is defined