Theme used for all icons in the chip.
If this is null and ThemeData.useMaterial3 is true, then IconThemeData with a ColorScheme.primary color and a size of 18.0 is used when the chip is enabled, and IconThemeData with a ColorScheme.onSurface color and a size of 18.0 is used when the chip is disabled. Otherwise, it defaults to null.
IconThemeData? get iconTheme;