Include field string keys on typedefs?

[kylebarron]

export type Point2 = arrow.FixedSizeList<arrow.Float> & {
  children: [arrow.Field<arrow.Float> & { name: "xy" }];
};

function tmp(x: arrow.DataType) {
  let z = x.children[0].name;
  // string
}
function tmp2(x: Point2) {
  let z = x.children[0].name;
  z
  // "xy"
}

Would provide a distinction between otherwise structurally-equal types (linestring--multipoint and polygon--multilinestring). Right now, if you pass in a multipoint type into a function like mapCoords you'll get linestring back