allow specifying a different content for adjacently tagged enums

[murl-digital]

i'm writing my own representation of the geojson format, and the rfc states that all geojson objects have a type field and all types have a coordinates field to store location data, except GeometryCollection, which is called geometries instead.

see: the examples

my proposed solution would look something like this:

#[derive(Serialize, Deserialize)]
#[serde(tag = "type", content = "coordinates")]
pub enum Geometry {
    Point(Position),
    MultiPoint(Vec<Position>),
    LineString(Vec<Position>),
    MultiLineString(Vec<Vec<Position>>),
    Polygon(Vec<Vec<Position>>),
    #[serde(content = "geometries")]
    GeometryCollection(Vec<Geometry>)
}

looking at what deserialize expands to, i can't immediately tell if this is doable