Implement Wikibase service clause

[D063520]

Part of the endpoint? (leave empty if you don't know)

• [X] Backend (hdt-qs-backend)
• [ ] Frontend (hdt-qs-frontend)
• [ ] Benchmark (hdt-qs-benchmark)
• [ ] Other

Description of the request

It would be nice to implement this SPARQL syntax that is not part of SPARQL 1.1 but which is a quasi standard since it is highly used in the Wikidata ecosystem. The most precise description of the specs I found is:

https://en.wikibooks.org/wiki/SPARQL/SERVICE_-_Label

Do I want to contribute to make it?

Yes

Something else?

No response

[D063520]

A first implementation was provided. This does not cover the full syntax but the most used part of it.