Reversal of coordinates

[teunbrand]

This PR aims to fix #4021 and fix #4801 and fix #5918.

Briefly, several coords get a reverse argument that can reverse the x/y/theta/r direction of a coord.

Importantly, this PR gets rid of the behaviour that giving the limits in reverse order implies transform = "reverse" in the scale, for the following reasons;

• This PR gives the reverse argument to get the same effect.
• The behaviour is undocumented.
• The behaviour is applies inconsistently.
• The behaviour is incompatible with other scale transformations, like date.
• The reversed limits had to be hardcoded, which makes the reversal gnarly to apply if not known a priori, especially for discrete or date scales.

The behaviour continues to work in xlim()/ylim() because that is the only place where it is documented.

Also worth noting:

• coord_radial(direction) was essentially doing the same thing, but just for 'theta'. This is now deprecated in favour of the reverse argument that works for both 'theta' and 'r'.
• guide_grid() has been rewritten to accommodate coord transformations/munching. This makes plots ~1ms slower to render.
  • As a consequence, coord_radial() now renders minor gridlines for the 'r' direction, which I didn't even realise were missing in the first place. This is the visual change you see in the snapshots.

Alright, some examples then. Reversing a discrete direction:

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

p <- ggplot(mpg, aes(class, hwy)) +
  geom_boxplot()

p + coord_cartesian(reverse = "x")

Showing that we can reverse transformed directions:

p + coord_trans(y = "sqrt", reverse = "y")

Showing that we can reverse directions for coord_sf():

world1 <- sf::st_as_sf(maps::map('world', plot = FALSE, fill = TRUE))
ggplot(world1) + 
  geom_sf() + 
  coord_sf(reverse = "xy")

Showing reversal for coord_radial(). Please note the anti-clockwise direction of 'theta' and outside-in direction of 'r', and preservation of the start/end angles.

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  coord_radial(
    start = 0.25 * pi, end = 1.5 * pi,
    reverse = "thetar"
  )

^{Created on 2024-09-02 with reprex v2.1.1}