Better font subset detection

We currently detect script subsets such as Arabic by counting the number of glyphs in the cmap table and then seeing if greater than 50% of them are in a specific script subset .nam file. Instead, what if we simply checked if a font fulfills a gflanguage base charset e.g for Arabic, we'd need all the base characters in https://github.com/googlefonts/lang/blob/main/Lib/gflanguages/data/languages/ar_Arab.textproto#L44?