GH-5327 Implementation of RDF 1.2 Triple Terms

[SarahGrand]

GH-5327

Implementation of RDF 1.2 triple terms, overwriting existing RDF-Star implementation.
Removed, deprecated, or disabled files and tests relating to RDF-Star that were no longer relevant for RDF 1.2.
Parsing and writing implemented only in Turtle, TriG, NTriples, and NQuads parsers.
SPARQL querying not implemented. SPARQL-Star functionality left as is, and needs to be updated for SPARQL 1.2.

Note: this PR also includes the changes for RDF 1.2 Literals (JSON and directed language strings) since some of these changes rely on code changes from that PR. RDF 1.2 Literals changes should be merged before this.

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• I've added tests for the changes I made
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[kenwenzel]

Thank you for the PR. I would propose to not restructure and change the version in one commit.
The first commit should restructure the code and the second commit could change the version.
We should also go to the version 6.0.0-SNAPSHOT and not 6.0.0