More sorting options for facet_wrap()

[teunbrand]

This PR aims to fix #5212.

Briefly, it adds more options for the dir argument to layout the panels in various ways. The as.table argument gets absorbed into dir when the previous way of declaring dir = "v" or dir = "h" is used.

The new options for dir are:

• "lt": start in the top-left, start filling left-to-right.
• "tl": start in the top-left, start filling top-to-bottom.
• "lb": start in the bottom-left, start filling left-to-right.
• "bl": start in the bottom-left, start filling bottom-to-top.
• "rt": start in the top-right, start filling right-to-left.
• "tr": start in the top-right, start filling top-to-bottom.
• "rb": start in the bottom-right, start filling right-to-left.
• "br" start in the bottom-right, start filling bottom-to-top

Using as.table with any of the options above has no effect.

As an example where blank panels are set at the beginning:

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

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  facet_wrap(~ class, dir = "rb")

^{Created on 2024-04-22 with reprex v2.1.0}

[thomasp85]

LGTM - Maybe add an example with the new features

[teunbrand]

Good idea thanks!