Add the "boxplot" type of nanoplot

[rich-iannone]

This adds another type of nanoplot, the box plot, bringing the selection up the three. These plots are laid out horizontally and by default the plots across rows share the same axis (since these are primarily meant for comparison across rows). Here's an example of how they look:

library(gt)
library(tidyverse)

dplyr::tibble(a = c(
  paste(rnorm(20, 20, 10), collapse = ","),
  paste(rnorm(100, 0, 5), collapse = ","),
  paste(rnorm(15, 8, 2), collapse = ","),
  paste(rnbinom(120, 10, 0.5), collapse = ","),
  paste(rnbinom(150, 5, 0.25), collapse = ",")
  )) %>%
  gt() %>%
  cols_nanoplot(columns = a, plot_type = "boxplot") %>%
  cols_hide(columns = a)

Hovering anywhere in the cell with a box plot will display the values.