Improve type-checking for JSON values

[rubensworks]

Issue type:

• ➕ Feature request

---

Description:

In 08b7950, we introduced the rdf:JSON param range, which allows users to pass arbitrary JSON values.
While useful for many cases, this strips away any kind of type-checking,
which may result in cases where an unexpected JSON shape is received.

Example where myParam expects a Record<string, string>:

{
  "@id": "ex:myInstance",
  "@type": "ex:MyClass",
  "ex:myParam": {
    "key1": "value1",
    "key2": "value2"
  }
}

So this would have to be converted into:

<ex:myInstance> a ex:MyClass;
  ex:myParam [ ex:key "key1"; ex:value "value1" ],
             [ ex:key "key2"; ex:value "value2" ].

AFAICS, JSON-LD currently doesn't support such functionality.

JSON-LD's property-based data indexing already gets us partially there (defining the key's as index range), but the keys would not allow direct values in that case.

[github-actions]

Thanks for the suggestion!