* fix(xslt): keep the literal prefix for xsl:namespace-alias, remap only the URI
XSLT 1.0 7.1.1: an aliased result element keeps the prefix used in the
stylesheet; only its namespace URI is replaced by the result namespace. The
serializer adopted the result-prefix as the output prefix, so axsl:foo aliased
to the XSLT namespace came out as xsl:foo. The result-prefix now only selects
the replacement namespace; the element name, attributes, and copied namespace
declarations all keep their literal prefix.
Closes Apache Xalan conformance cases namespace19, namespace23, namespace24, namespace35, namespace113.
* refactor(xslt): drop the now-unused NamespaceAlias prefix field
The namespace-alias output keeps the literal prefix, so the result-prefix is no
longer stored; only the result namespace URI is needed. Removes the dead field
and corrects the addNamespaceAlias doc comment.