Additional arrow.fill parameters for line-based functions.

[teunbrand]

This PR aims to fix #5658.

Briefly, an arrow.fill parameter was either added or propagated in these functions:

• geom_path() and thus by extension geom_line()
• geom_function()
• geom_sf() when drawing line geometries
• element_line()

A demonstration of each of these:

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

my_arrow <- arrow(angle = 20, type = "closed")

ggplot(pressure, aes(temperature, pressure)) +
  geom_line(arrow = my_arrow, arrow.fill = "red")

ggplot() +
  geom_function(
    fun = dnorm, xlim = c(-2, 2), 
    arrow = my_arrow, arrow.fill = "red"
  )

ggplot(sf::st_linestring(as.matrix(pressure))) +
  geom_sf(arrow = my_arrow, arrow.fill = "red")

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  theme(
    axis.line = element_line(arrow = my_arrow, arrow.fill = "red")
  )

^{Created on 2024-03-11 with reprex v2.1.0}

[thomasp85]

LGTM

[teunbrand]

@thomasp85 Found out that geom_step() didn't have arrow settings either, so I included this function to.
I'll re-request a review.

[thomasp85]

LGTM