Verify proof-embedded capability delegation RDF consistency

[clehner]

The verify_proof_consistency function (added in #241) calls match_list_property to check that a proof object's JSON(-LD) corresponds to its RDF data:

ssi/src/vc.rs

Lines 2269 to 2276 in 3fc36d8

	graph_ref.match_list_property(
	proof_id,
	"https://w3id.org/security#capabilityChain",
	proof
	.property_set
	.as_ref()
	.and_then(|cc| cc.get("capabilityChain")),
	)?;

But this expects that the capabilityChain proof property if present contains an array of URIs (IRIs). The check fails when an embedded delegation object exists in the array. To allow embedded delegations in the capabilityChain array, the check in verify_proof_consistency needs to be relaxed or improved to handle this case.