Dotplots with discrete y

[teunbrand]

This PR aims to fix #5462.

Briefly, it brings the behaviour of swapping x and y in geom_dotplot() closer to what coord_flip() does.

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2

swapped <- ggplot(data = iris) +
  geom_dotplot(aes(x = Sepal.Length, y = Species), binaxis = "x") +
  ggtitle("Swapped aesthetics")

flipped <- ggplot(data = iris) +
  geom_dotplot(aes(x = Species, y = Sepal.Length), binaxis = "y") +
  coord_flip() +
  ggtitle("With `coord_flip()`")

library(patchwork)
swapped + flipped
#> Bin width defaults to 1/30 of the range of the data. Pick better value with
#> `binwidth`.
#> Bin width defaults to 1/30 of the range of the data. Pick better value with
#> `binwidth`.

^{Created on 2023-10-09 with reprex v2.0.2}

[thomasp85]

LGTM