Added assertion up to cv99 for FontFeature.characterVariant (#27745)

* Added assertion up to cv99 for FontFeature.characterVariant

* Added FontFeature.characterVariant(99) test

Author: Darkade

lib/ui/text.dart

@@ -472,7 +472,7 @@ class FontFeature {
   ///  * <https://docs.microsoft.com/en-us/typography/opentype/spec/features_ae#cv01-cv99>
   factory FontFeature.characterVariant(int value) {
     assert(value >= 1);
-    assert(value <= 20);
+    assert(value <= 99);
     return FontFeature('cv${value.toString().padLeft(2, "0")}');
   }
 

testing/dart/text_test.dart

@@ -198,6 +198,7 @@ void testFontFeatureClass() {
     expect(const FontFeature.caseSensitiveForms(), const FontFeature('case', 1));
     expect(      FontFeature.characterVariant(1), const FontFeature('cv01', 1));
     expect(      FontFeature.characterVariant(18), const FontFeature('cv18', 1));
+    expect(      FontFeature.characterVariant(99), const FontFeature('cv99', 1));
     expect(const FontFeature.denominator(), const FontFeature('dnom', 1));
     expect(const FontFeature.fractions(), const FontFeature('frac', 1));
     expect(const FontFeature.historicalForms(), const FontFeature('hist', 1));