fix(export): own a declaration head's relationships in the order the notation spells them

changes/unreleased/declaration-head-owned-relationship-order.fixed.md

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+- The RDF and API JSON writers own a declaration head's relationships in the order the notation spells them: a usage's typings, specializations and multiplicity come first in `ownedRelationship` as written (`:>> x : T = v` owns its Redefinition, then its FeatureTyping, then its FeatureValue), ahead of the value and the body members, and a definition's Subclassification ahead of its members; `ownedSpecialization` and the other owned-relationship lists follow the same order. `Element::ownedRelationship` is ordered (KerML 8.3.2.1.2) and the textual notation adds each owned relationship as it parses the clause (KerML 8.2.1, SysML 8.2). The reader spells a head back in the order the graph owns its relationships, the multiplicity part included, instead of a fixed clause order. Where a head relates one target under two clauses that materialize as the same class (`subsets x specializes x`), the writer states each element's keyword as `sysx:headClause`, so the two come back apart and in order under either id form; a multiplicity no membership places is written once, with the first typing clause.