position_points_sina: Randomly distribute points in a ridgeline plot between baseline and ridgeline
Description
This is a position adjustment specifically for geom_density_ridges() and related geoms. It
only jitters the points drawn by these geoms, if any. If no points are present, the plot
remains unchanged. The effect is similar to a sina plot: Points are randomly distributed to fill
the entire shaded area representing the data density.