Very different behavior on iterators compared to RMLViewer + RMLMapper

Following up on #3, but using LogicalViews, there's a big gap between what MappingWeaver allows to access array values, versus what RMLViewer + RMLMapper allow.

Given the following scaffolding:

:view a rml:LogicalView ;
  rml:viewOn [
    # JSONPath root iterator over { "key": [ "1", "2" ] }
  ] ;
  rml:field [
    rml:fieldName "key"
    # insert field definition from list below
  ] .

:mapping a rml:TriplesMap ;
  rml:logicalSource :view ;
  rml:subjectMap [ rml:termType rml:BlankNode ] ;
  rml:predicateObjectMap [
    rml:predicate <urn:example:hasValue> ;
    rml:objectMap [ 
      # insert corresponding reference from field definitions below
    ]
  ] .

A. With direct reference rml:reference "key" in the mapping:

• rml:reference "key[*]" in the view's field works
• rml:reference "$.key[*]" in the view's field works
• rml:reference "key" in the view's field fails in MappingWeaver
• rml:reference "$.key" in the view's field fails in MappingWeaver
• rml:iterator "$.key[*]" (without nested field) fails in MappingWeaver and RMLViewer+RMLMapper

B. With nested reference rml:reference "key.value" in the mapping:

1. Using rml:iterator "$.key[*]" ; rml:field [ rml:fieldName "value" ; ... ] in the view:

• rml:reference "@" in the nested field works (and MappingWeaver adds canonical type)
• rml:reference "[*]" in the nested field fails in MappingWeaver
• rml:reference "$" in the nested field fails in MappingWeaver

2. Using rml:iterator "key[*]" [ rml:fieldName "value" ; ... ] in the view, all of the references above (@, [*], $) fail in MappingWeaver

3. Using rml:iterator "$.key" [ rml:fieldName "value" ; ... ], in the view, all of the references above fail in MappingWeaver

4. Using rml:iterator "key" [ rml:fieldName "value" ; ... ], in the view, all of the references above fail in MappingWeaver

Start by reproducing the supplied LogicalViews scaffolding and the iterator/reference cases, then trace how MappingWeaver handles nested fields and array values. Compare the results with RMLViewer and RMLMapper; done means the differing cases have an agreed, tested behavior or the incompatibility is clearly documented.