NumberList: Don't use the Parse trait; implement similar methods directly
NumberList: Don't use the Parse trait; implement similar methods directly

NumberList::parse() and parse_str() are used in a couple of places,
but we'll pass the NumberListLength argument directly, rather than
relying on the Data associated type in Parse.

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg