add the `sh:` prefix

[VladimirAlexiev]

• I think that SHACL is a lot more widely used than some of the ones in the current list (https://w3c.github.io/json-ld-rc/prefixes.ttl)
• Make sh:prefixes optional in SPARQL queries data-shapes#176 discusses how to make sh:prefixes less necessary.
• One may not need to use sh in SHACL SPARQL, but I still think it makes sense to add it

[TallTed]

What was the content of https://w3c.github.io/json-ld-rc/prefixes.ttl based on? And what puts it to use?

Why not include all the prefixes from prefix.cc (here as a JSON-LD @context)? Or get the full list (available as txt, csv, and others (see the footer on this page)) in order of "popularity", and pick the count you want?

[gkellogg]

The files are written from the rdfa-1.1.html document via a GitHub action (see README). This source services the needs of both the RDFa Initial Context and the JSON-LD Recommended Context.

Previously, we had said that any W3C Recommendation that defines a namespace/prefix pair can be included in this context. This supports adding "sh" as the prefix for the SHACL namespace <http://www.w3.org/ns/shacl#>.

prefix.cc defines its own context at https://prefix.cc/context.