Support entity text indexes

[der]

[This depends on a decision to invest in entity text indexes generally.]

Assuming a source with an entity-style text index then the dsapi could move multiple parts of the query into the text index. Needs some means of annotating Aspect declarations to say how they map to index fields (including handling property paths).

If the entity index includes numeric/date fields then the dsapi could also potentially move some range queries into the entity index.

Consider whether some form of query hinting would also be useful to control use of text index v.s. SPARQL on a per query basis.

[ijdickinson]

It seems like we de facto decided not to do this. Should we close this issue now?