Function get_known_child_positions 

fn get_known_child_positions(
    placements: &[InBothAbsAxis<Line<GenericGridPlacement<OriginZeroLine>>>],
) -> (OriginZeroLine, OriginZeroLine, u16, OriginZeroLine, OriginZeroLine, u16)

Iterate over the children’s grid-row/grid-column styles (named lines resolved), producing an estimate of the min and max grid lines along with the span of each item

Min and max grid lines are returned in origin-zero coordinates) The span is measured in tracks spanned