With purl v0.2.1, FullName returns a Swift package as its registry
identity, scope.name. The mirror splits namespace/name again to find
the scope or the source repository, so HandlerPackage keeps that form,
as mirrorTarget did before the two mappings were shared.
packageurl.HandlerPackage returns the ecosystem and name the handlers store
a package URL under. The mirror and the inventory both use it, which
settles where they disagreed: distribution namespaces of apk, alpm, bsd,
deb and rpm are dropped, PyPI and NuGet names use purl's comparison form,
and Maven names are group:artifact as the handler stores them, where the
mirror used group/artifact.
