UIFontDescriptor for SF UI high-legibility figures

SFUI-HighLegibilityFontDescriptor.swift

func fontDescriptorWithHighLegibilityMonospacedFigures(for fontDescriptor: UIFontDescriptor) -> UIFontDescriptor {
   return fontDescriptor.addingAttributes(
       [
           UIFontDescriptor.AttributeName.featureSettings:
               [
                   [   // High legibility 6 and 9
                       UIFontDescriptor.FeatureKey.featureIdentifier: kStylisticAlternativesType,
                       UIFontDescriptor.FeatureKey.typeIdentifier: kStylisticAltOneOnSelector,
                   ],
                   [   // High legibility 4
                       UIFontDescriptor.FeatureKey.featureIdentifier: kStylisticAlternativesType,
                       UIFontDescriptor.FeatureKey.typeIdentifier: kStylisticAltTwoOnSelector,
                   ],
                   [
                       UIFontDescriptor.FeatureKey.featureIdentifier: kNumberSpacingType,
                       UIFontDescriptor.FeatureKey.typeIdentifier: kMonospacedNumbersSelector
                   ]
             ]
         ]
   )
}