A list of
FontFeatures that affect how the font selects glyphs.
Some fonts support multiple variants of how a given character can be
rendered. For example, a font might provide both proportional and
tabular numbers, or it might offer versions of the zero digit with
and without slashes.
FontFeatures can be used to select which of
these variants will be used for rendering.
final List<ui.FontFeature>? fontFeatures;