Function join_v 

pub fn join_v(grids: &[Grid]) -> Grid

Stack grids top-to-bottom into one Grid (layer 0 only).

The result’s height is the sum of the input heights; its width is the widest input. Each grid is placed left-aligned; cells past a narrower grid’s width are left untouched (empty, per Grid::new’s default tiles). For an empty slice, returns a 1-wide, 0-tall grid: see join_h for why a zero-width grid isn’t representable.