Match the named list portion of
(vl-parse-1+-named-property-list-of-arguments &key (tokstream 'tokstream) (config 'config)) → (mv errmsg? value new-tokstream)
See vl-parse-property-list-of-arguments. Our goal here is
to parse the named arguments in the tail of a
'.' identifier ( [property_actual_arg] ) { ',' '.' identifier ( [property_actual_arg] ) }