function computeEdgeNormals(plane, vertices) {
  const edgeNormals = [];
  for (let i = 0; i < 4; i++) {
    edgeScratch = Cartesian3.subtract(
      vertices[(i + 1) % 4],
      vertices[i],
      edgeScratch,
    );
    edgeNormalScratch = Cartesian3.cross(
      plane.normal,
      edgeScratch,
      edgeNormalScratch,
    );
    edgeNormalScratch = Cartesian3.normalize(
      edgeNormalScratch,
      edgeNormalScratch,
    );
    edgeNormals[i] = Cartesian3.clone(edgeNormalScratch);
  }
  return edgeNormals;
}
Compute edge normals on a plane.
@private