Deprecate fatten

[teunbrand]

This PR aims to fix #4881.

Briefly it deprecates fatten in geom_pointrange() (per linked issue), but also geom_boxplot() and geom_crossbar().
The parameter still works as it used to, but this at least starts the deprecation process.
There is a slight hiccup in geom_boxplot() as it isn't a named argument, but we check for if the argument has been picked up in the parameters.

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

df <- data.frame(
  trt = factor(c(1, 1, 2, 2)),
  resp = c(1, 5, 3, 4),
  group = factor(c(1, 2, 1, 2)),
  upper = c(1.1, 5.3, 3.3, 4.2),
  lower = c(0.8, 4.6, 2.4, 3.6)
)

p <- ggplot(df, aes(x = trt, y = resp, col = group, ymin = lower, ymax = upper))

ggplotGrob(
  p + geom_pointrange() + 
    geom_crossbar() + 
    geom_boxplot()
) |> invisible()

ggplotGrob(
  p + geom_pointrange(fatten = 1) + 
    geom_crossbar(fatten = 1) + 
    geom_boxplot(fatten = 1)
) |> invisible()
#> Warning: The `fatten` argument of `geom_pointrange()` is deprecated as of ggplot2 3.6.0.
#> ℹ Please use the `size` aesthetic instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
#> Warning: The `fatten` argument of `geom_crossbar()` is deprecated as of ggplot2 3.6.0.
#> ℹ Please use the `middle.linewidth` argument instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
#> Warning: The `fatten` argument of `geom_boxplot()` is deprecated as of ggplot2 3.6.0.
#> ℹ Please use the `median.linewidth` argument instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.

^{Created on 2024-12-12 with reprex v2.1.1}

[thomasp85]

LGTM