xsd:anyURI is sameValueAs an xsd:string or simple literal

In the memory model xsd:anyURI matches in Graph.find an xsd;string with the same lexical form.

"http://example/"^^{xsd:anyURI matches "http://example/"}^xsd:string and "http://example/"

This is because the value returned by Xerces is a Java string and isEqual in XSDDatatype is based on equality of Xerces value regerdless of datatype to account for derived types.

The proposed solution in the patch is to have a new XSD datatype that uses the BaseDatatype isEquals machinery which makes equity "same datatype, same value".

Also applies to xsd:QName, xsd:IDREF, xsd:NOTATION