Metadata Editor does not used the user-supplied property IRI for attribute-value fields when generating an instance

[martinjoconnor]

If I have an attribute-value field in a template or element and explicitly set the property IRI for that field, the generated instance should use that property IRI for all user-supplied fields for that attribute-value in the instance.

For example, if we have an attribute-value field "AV" with https://example.com/p1 set as its property IRI and we have two user-supplied fields "AVF1" and "ACF2" for that attribute-value in the instance then the JSON-LD should be:

 "@context": {
    "AVF1": "https://example.com/p1",
    "AVF2": "https://example.com/p1"
 }
 ...
 "AV": [ "AVF1", "AVF2" ],
 ...
 "AVF1": { "@value": "value 1" },  
 "AVF2": { "@value": "value 2" }
}

Currently, a property IRI is auto-generated for each user-supplied field instead of using the specified property IRI.