fix: respect width aesthetic

[Yunuuuu]

fix #6575

n <- vapply(
    split(mpg, ~cyl),
    function(d) length(unique(d$class)),
    integer(1L)
)

dplyr::mutate(mpg,
    width = length(unique(class)),
    median = length(unique(class)) / 2L,
    .by = cyl
) |>
    ggplot() +
    geom_boxplot(
        aes(median, hwy, group = median, width = width)
    ) +
    facet_wrap(vars(cyl), nrow = 1L, space = "free_x", scales = "free_x") +
    ggh4x::facetted_pos_scales(
        lapply(n, function(max) scale_x_continuous(limits = c(0, max)))
    )

[teunbrand]

I would like to add optional_aes = "width" to the StatBoxplot class, if we're going to treat it as an aesthetic.

[teunbrand]

Lovely, thank you for adopting the proposals!
If you want, you can add a bulletpoint to the news file

[Yunuuuu]

It seems this PR is based on an older version of ggplot2, and the NEWS.md file conflicts with the current version. Therefore, I chose not to add the news item to NEWS.md.

[teunbrand]

The typical remedy for this type of situation is to update your fork and merge the (updated) main branch into the PR branch.
I'm happy to add the news bullet if you'd prefer that.

[Yunuuuu]

Thanks for the suggestion! Please feel free to add the news bullet directly.

[teunbrand]

Thank you for the contribution!