Revisit URI validation

[nichtich]

SSSOM Type URI is actually based on xsd:anyURI which is based on RFC 3987 (IRI) instead of RFC 3986 (URI).

Test case:

• IRI https://example.com/ü
• URI: https://example.com/%C3%BC

[nichtich]

As discussed here, relative IRIs are allowed, translating to file:// by default. Resolution requires to pass a base URI as parameter and relative URIs should result in warnings at least.

[nichtich]

As discussed at mapping-commons/sssom#448 the URI slots must be absolute URIs, so no need to pass a base URI for resolution.