Add hoverable data values for single-bar nanoplots

[rich-iannone]

This PR makes single-bar nanoplots display their values on hover. As these types of nanoplots can have a mix of positive, negative, and zero-value bars, it was important to ensure that the compactly-formatted data values are affixed to the zero-line, with the text anchored on the appropriate side. Zero value labels were adjusted to lie in a more central position (since there is no bar). The user could hover virtually anywhere in the cell and the value will then appear (i.e., the hover area is large for convenience).

Here we also add the interactive_data_values argument to the nanoplot_options() function. This allows for having persistent data values shown on the single-bar nanoplots. This may be desirable in some cases since there is only a single value per nanoplot (i.e., clutter won't be an issue) and having a compactly formatted value present is commonly seen in bar plots.

Here is an example of this:

dplyr::tibble(
  a = c(-20, -10, 0, 10, 5)
) |>
  gt() |>
  cols_nanoplot(
    columns = a,
    plot_type = "bar",
    options = nanoplot_options(
      data_bar_negative_fill_color = "lightblue",
      data_bar_fill_color = "lightgreen",
      data_bar_stroke_color = "forestgreen",
      data_bar_negative_stroke_color = "steelblue",
      interactive_data_values = FALSE
    )
  ) |>
  tab_style(
    style = cell_borders(sides = c("left", "right"), weight = "2px"),
    locations = cells_body(columns = nanoplots)
  )

If that option is unset or TRUE (i.e., the default display) we get this:

where the screenshot was taken while hovering over the second nanoplot.

Fixes: #1517