Places the groups that set_color() creates beside each other, on top of
each other, or stretched to fill the axis. A chart with a single group has
nothing to arrange, so this does nothing until a colour column other than
x splits it.
Examples
df <- data.frame(
species = c("a", "a", "b"),
island = c("x", "y", "x")
)
arc_bar(df, species) |>
set_color(island) |>
set_position("stack")