Allow `plot()`ting

[matt-dray]

Let users add plots to the hex with plot(). This is possible already in theory, but might need to consider any interactions with open viewports, etc.

[matt-dray]

Probably requires a package like gridBase() to make a plot() a grob?

[matt-dray]

This achieves what I want with {ggplotify}, but relies also on {gridGraphics}:

temp_path <- tempfile(fileext = ".png")
hexbase::open_device(temp_path)
hexbase::add_hex(0, , "grey")
grid::pushViewport(grid::viewport())
x <- ggplotify::base2grob(
  \() {
    par(mar = rep(0, 4))
    n <- 100
    plot(
      runif(n), runif(n),
      xaxs = "i", yaxs = "i",
      axes = FALSE, ann = FALSE,
      pch = 16, col = palette.colors(n, , , TRUE)
    )
  }
)
grid::grid.draw(x)
grid::popViewport()
hexbase::close_device()
system(paste("open", temp_path))