Support RDF 1.2

RDF 1.2 includes:

* Triple terms
* Reification by `rdf:refies` (and other properties)

This is not the [RDF-star CG report](https://w3c.github.io/rdf-star/cg-spec) but the way the Working Group has structured the changes means that the impact on Turtle is significantly reduced.

As well as RDF-star:
* Errata for RDF 1.2 and SPARQL 1.1
* Initial text direction, a new facet of an RDF term: only for language strings: example`"قطة"@ar--rlt`
* Defined canonical output of N-triples and N-quads (for RDF Canonicalization)
* `rdf:JSON` datatype as part of core RDF

RDF 1.2 / SPARQL 1.2 is compatible with RDF 1.1 / SPARQL 1.1.