[PoC] Import decisions and BKMs from another DMN

[saig0]

Description

This is a proof-of-concept (PoC) to see how we could import decisions and BKMs from another DMN file.

The general idea:

• Store parsed decisions/BKMs in a repository.
• Ignore imported decisions/BKMs during the parsing.
• On evaluation, load the imported decisions/BKMs from the repository.

Open to-do's:

• [x] Move the loading of imported decisions/BKMs from the parser to the evaluation logic. The import is part of the evaluation.
• [x] Handle decisions/BKMs with namespaces natively (i.e. qualified names). Don't modify the name.
• [ ] Evaluate imported decisions/BKMs differently by wrapping them into a FEEL context. The evaluation interprets the qualified name as a path expression.
• [x] Handle the case if an imported decision/BKM is not present. Don't throw exceptions.
• [ ] Document the new public API.
• [ ] Write more test cases to cover edge cases.
• [ ] Fix the InvocationTest.scala. Out of scope for this PR because the test was not really correct before.

Related issues

related to #71

[saig0]

I merged #225 into the branch and rebased it on main. :building_construction: