Fill in missing se parameter

[teunbrand]

This PR aims to fix #5572 and amends #2567.

Briefly, instead of setting a default se = FALSE in GeomSmooth$draw_group(), we let the default se depend on the presence of ymin and ymax columns in GeomSmooth$setup_params(). This allows specifying a layer with geom = "smooth" to automatically infer the standard behaviour.

Of all examples in #2567, only the following has changed. Previously, no ribbons would be drawn because stat_summary() does not have an se parameter. Now, se = TRUE is inferred due to presence of ymin/ymax columns.

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

ggplot(mtcars, aes(cyl, mpg, fill = factor(am))) +
  stat_summary(geom = "smooth")
#> No summary function supplied, defaulting to `mean_se()`

^{Created on 2024-02-22 with reprex v2.1.0}

[thomasp85]

LGTM