Repurpose coord expansion

[teunbrand]

This PR aims to fix #6020.

Briefly, it allows expand to take a length-4 logical vector for each of the positions (top, right, bottom, left).
Alternatively, one could use a named vector too.

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

# Showing logical vector
ggplot(mpg, aes(class)) +
  geom_bar() +
  coord_cartesian(expand = c(TRUE, TRUE, FALSE, TRUE))

# Showing named vector
ggplot(mpg, aes(y = class)) +
  geom_bar() +
  coord_cartesian(expand = c(left = FALSE))

^{Created on 2024-08-05 with reprex v2.1.1}

[thomasp85]

I like this idea

[thomasp85]

Not sure flipping the coord params is the logical solution here

[teunbrand]

In this PR, coord_flip(expand = c(left = FALSE)) removes the left expansion, which feels correct to me. I don't know how much this intuition holds, but I feel like coord_flip() swaps x/y, but not left/bottom and right/top.
I'm unsure whether there is a more logical solution available here.