Custom inside-axis position for coord_radial()

[teunbrand]

This PR aims to fix #5805.

Briefly, you can now use numeric values for coord_radial(r.axis.inside) that will place the radius axis at some specified position of the theta axis.

I think it is probably best illustrated how it works.
Let's make plot with clock-positions.

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

set.seed(42)
df <- data.frame(x = runif(100, max = 12), y = rnorm(100))

p <- ggplot(df, aes(x, y)) +
  geom_point() +
  scale_x_continuous(limits = c(0, 12), breaks = 1:12, expand = c(0, 0)) +
  theme(axis.line = element_line())

This is how one would set the position:

p + coord_radial(r.axis.inside = 4.5)

If for some reason you have secondary axes, you can set a vector to control primary and secondary separately.

p + coord_radial(r.axis.inside = c(4.5, 7)) +
  guides(r.sec = "axis")

Out of bounds axes get squished to the nearest limit.

p + coord_radial(r.axis.inside = -10)

^{Created on 2024-05-24 with reprex v2.1.0}