Add SHACL path to RDFLib Path utility and corresponding tests

[mgberg]

Summary of changes

This adds a utility to parse valid SHACL Paths (e.g. the objects of triples with predicate sh:path) into an RDFLib-friendly object. The resulting object could either be:

• A URIRef, when the path is simply a predicate
• A Path, when the path is complex (e.g. [sh:inversePath skos:broader])

This enables easy evaluation and manipulation of SHACL paths using RDFLib. For example:

• The output can be passed to any of several methods (Graph.triples, Graph.value, etc.) as a predicate to get value(s) at that path
• The n3 method can be used to get a SPARQL property path representation of the path

Note that pyshacl does not have a utility to do this- rather, it only evaluates SHACL paths.

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Checked that all tests and type checking passes.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[coveralls]

coverage: 90.964% (+0.02%) from 90.943%
when pulling 3b6ded5 on mgberg:shacl-path-parser
into ce7e414 on RDFLib:main.

[nicholascar]

Would be good to see more than just one utility function for a "Utilities" SHACL file!

[mgberg]

Would be good to see more than just one utility function for a "Utilities" SHACL file!

Agreed!