Ensure that supplied locale is normalized when creating an interactive table

[rich-iannone]

When using an interactive table, the locale value (supplied in the initial gt() call) is retrieved in order to display elements/controls in the language of the locale. However, there are a few ways to write a locale and internally normalize_locale() is used to standardize a provided locale to a chosen form.

This wasn't done in the codepath for making an interactive table so using "fr_CH" instead of "fr-CH" would have resulted in english text (the result of a failed lookup). This PR ensures that the locale value is normalized so the following code works as expected:

library(gt)
library(tidyverse)

mtcars |> 
  mutate(mpg = mpg*1000) |> 
  gt(locale = "de_CH") |> # or "fr_CH"
  fmt_number(mpg, decimals = 2) |>
  opt_interactive()

Fixes: #1637