port lint should warn about unknown licenses

[ryandesign (Ryan Carsten Schmidt)]

port lint already warns when a port doesn't set a license but it would be an improvement if it could catch typos or other errors in license names. This would require that the list of known distributable license names be moved to a place where MacPorts base could read it (see #60315) and would require adding to it a list of known nondistributable licenses.