Slice 5 of #92. The last validator moves onto the framework and the legacy
Issue type is removed, so all validation now flows through one error model.
- ValidationError gains a severity (error by default, warning for advisory
findings), chosen so Schematron's assert/report distinction survives in the
unified type.
- Schematron is a Validation<Node, Void> over the document root; a failed assert
is an error finding, a matched report a warning. Each finding is located at the
context node its rule fired on (built from the element chain, with a sibling
index only when a name repeats), not the document root.
- Schematron.validate returns [ValidationError] and runs through a Validator.
- Validation.Issue and its Severity-based result are deleted; Severity now backs
ValidationError.
Every validation layer (structural, DTD, XSD content and identity, Schematron)
now produces located ValidationError values through the shared framework.
Mihaela Mihaljevic
d682f85daf