Enhancement: Replace WCAG contrast with APCA algorithm in `_ideal_fgnd_color()`

[juleswg23]

See this PR: rstudio/gt#1062

And the corresponding R code:

https://github.com/rstudio/gt/blob/0d3012c7124dc057b88667a24653f1ce6e2331fc/R/utils_color_contrast.R#L117-L130