New label_glue() function

[teunbrand]

This PR aims to fix #457.

Briefly, a new label_glue() function is added that uses the glue package to interpolate strings. The only thing users familiar with the glue package should know is that x is the variable that holds the breaks values.

devtools::load_all("~/packages/scales/")
#> ℹ Loading scales
demo_discrete(iris$Species, labels = label_glue("The Iris {x} flower"))
#> scale_x_discrete(labels = label_glue("The Iris {x} flower"))

^{Created on 2024-10-07 with reprex v2.1.1}

@thomasp85 are there some steps to take that will make {marquee} integration more useful?

[teunbrand]

Added option to parse the labels to expressions:

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

demo_continuous(c(0, 10), labels = label_glue("'{number(x)}m'^2", parse = TRUE))
#> scale_x_continuous(labels = label_glue("'{number(x)}m'^2", parse = TRUE))

demo_log10(c(1, 1e4), labels = label_glue("10^{log10(x)}", parse = TRUE))
#> scale_x_log10(labels = label_glue("10^{log10(x)}", parse = TRUE))

^{Created on 2024-10-11 with reprex v2.1.1}