Add position_jitterdodge(preserve) argument

[teunbrand]

This PR aims to fix #6584.

It includes the preserve logic analogous to position_dodge(), as well as the order aesthetic.
Reprex from issue:

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

ggplot(penguins, aes(species, bill_len, fill = island)) +
  stat_summary(
    geom = "bar",
    fun = "mean",
    show.legend = T,
    position = position_dodge(preserve = "single")
  ) +
  stat_summary(
    geom = "errorbar",
    fun.data = "mean_sdl",
    fun.args = list(mult = 1),
    width = 0.3,
    position = position_dodge(width = 0.9, preserve = "single")
  ) +
  geom_point(
    show.legend = F,
    position = position_jitterdodge(
      jitter.width = 0.3, dodge.width = 0.9, preserve = "single"
    )
  )
#> Warning: Removed 2 rows containing non-finite outside the scale range
#> (`stat_summary()`).
#> Removed 2 rows containing non-finite outside the scale range
#> (`stat_summary()`).
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

^{Created on 2025-10-02 with reprex v2.1.1}