Enhance `select` Syntax to Allow `datatype` References in Graph-Crawl Queries

[aaj3f]

Description

Related to #713 -- use of datatype in where clauses (e.g. with bind) can only surface those results if the select statement directly returns bindings from where.

Often, users use the select statement to perform graph crawls off of subject bindings from the where clause. We should make sure that in this scenario, it is possible to return results that indicate the datatype of each value, for example:

...
"select": {
  "?s": [
    "schema:name", 
    { "@id": "arbitraryValues", "withDataType": true }
  ]
},
...

This may not be the desire syntax at all, but the goal is to allow users to describe particular properties in the query that they want to see datatype (and value) results for