Support serializing individuals as string with context info

[ledsoft]

As a developer, I want to be able to make JSON-LD output as close to plain JSON as possible. This should include the ability to serialize individuals (plain identifier object property values as well as enum constants mapped to individuals) as string with info about the value being in identifier in the context.

For example, currently, an individual is serialized as an object with id:

{
  "@context": {
    "attribute": "http://example.org/attribute"
  },
  "attribute": {
    "@id": "http://www.w3.org/2002/07/owl#ObjectProperty"
  } 
}

Instead, it should be possible to configure the serialization (with context) so that the output is as follows:

{
  "@context": {
    "attribute": {
      "@id": "http://example.org/attribute",
      "@type": "@id"
    }
  },
  "attribute": "http://www.w3.org/2002/07/owl#ObjectProperty"
}

This should make it easier for clients to digest the JSON-LD. Note that this will not have any influence on deserialization and serialization without context.

[ledsoft]

Note that this is described as Expanded term definition in the JSON-LD specification.