Implement geom_linerange(arrow) and geom_pointrange(arrow)

[teunbrand]

This PR aims to fix #6481.

Briefly, it adds the arrow and arrow.fill arguments to the geoms mentioned in the title.
Examples:

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

df <- data.frame(
  trt = c("A", "A", "B", "B"),
  resp = c(1, 5, 3, 4),
  group = factor(c(1, 2, 1, 2)),
  upper = c(1.1, 5.3, 3.3, 4.2),
  lower = c(0.8, 4.6, 2.4, 3.6)
)

staple <- arrow(angle = 90, length = unit(2, "mm"), ends = "both")

p <- ggplot(df, aes(trt, resp, colour = group, ymin = lower, ymax = upper))
p + geom_linerange(arrow = staple)

p + geom_pointrange(arrow = staple)

^{Created on 2025-05-27 with reprex v2.1.1}

[thomasp85]

NEWS bullet? otherwise LGTM