Legend keys

[teunbrand]

This PR aims to fix #111.

Briefly, it adds a new function: draw_key_richtext() that can draw legend keys with formatted text. As a demonstration, we can render a similar reprex to the one given in #111:

library(ggplot2) # dev version
devtools::load_all("~/packages/ggtext/")
#> ℹ Loading ggtext

ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) +
  geom_point(key_glyph = 'richtext') +
  scale_colour_discrete(
    labels = NULL,
    guide = guide_legend(override.aes = list(
      label = paste0(
        "<i><span style='color:black'>Iris</span> ", 
        c("setosa", "versicolor", "virginica"), "</i>"
      ),
      size = 11 / .pt, hjust = 0, label.colour = NA
    ))
  )

^{Created on 2023-12-16 with reprex v2.0.2}

There are a few questions/remarks I have about how to proceed:

• As a remark, the function was designed with Custom key glyph sizes tidyverse/ggplot2#5465 in mind.
• Should this be the default key for geom_richtext() and geom_textbox()?
• The visual test only makes sense with the development version of ggplot2.
• I didn't see any actual snapshots of the visual tests in the testthat folder. Should I omit the svg file that the included snapshot test generates?

Thanks for reading!

[teunbrand]

These steps are necessary to ensure that the grobs stay within their designated area when the angle is not 0.
Here is an example if I omit these lines:

[clauswilke]

I think this can be the default key glyph if it's backwards compatible. I don't know what the status of visual tests is. Haven't looked into it in a long time. I had tons of issues with visual tests (as they would always break with any minor update in the rendering stack), so I've mostly given up on them.

Also, looks like the CI framework is outdated and needs to be fixed before tests pass.