Add fallback font to IconData class (#127269)

This PR adds an ability to specify `fallbackFont` for `Icon` class via `IconData` props.

Read detailed description here https://github.com/flutter/flutter/issues/126670

packages/flutter/lib/src/widgets/icon.dart

@@ -280,6 +280,7 @@ class Icon extends StatelessWidget {
           fontSize: iconSize,
           fontFamily: icon!.fontFamily,
           package: icon!.fontPackage,
+          fontFamilyFallback: icon!.fontFamilyFallback,
           shadows: iconShadows,
         ),
       ),

packages/flutter/lib/src/widgets/icon_data.dart

@@ -31,6 +31,7 @@ class IconData {
     this.fontFamily,
     this.fontPackage,
     this.matchTextDirection = false,
+    this.fontFamilyFallback,
   });
 
   /// The Unicode code point at which this icon is stored in the icon font.
@@ -56,6 +57,11 @@ class IconData {
   /// [Directionality] is [TextDirection.rtl].
   final bool matchTextDirection;
 
+  /// The ordered list of font families to fall back on when a glyph cannot be found in a higher priority font family.
+  ///
+  /// For more details, refer to the documentation of [TextStyle]
+  final List<String>? fontFamilyFallback;
+
   @override
   bool operator ==(Object other) {
     if (other.runtimeType != runtimeType) {
@@ -65,11 +71,20 @@ class IconData {
         && other.codePoint == codePoint
         && other.fontFamily == fontFamily
         && other.fontPackage == fontPackage
-        && other.matchTextDirection == matchTextDirection;
+        && other.matchTextDirection == matchTextDirection
+        && listEquals(other.fontFamilyFallback, fontFamilyFallback);
   }
 
   @override
-  int get hashCode => Object.hash(codePoint, fontFamily, fontPackage, matchTextDirection);
+  int get hashCode {
+    return Object.hash(
+      codePoint,
+      fontFamily,
+      fontPackage,
+      matchTextDirection,
+      Object.hashAll(fontFamilyFallback ?? const <String?>[]),
+    );
+  }
 
   @override
   String toString() => 'IconData(U+${codePoint.toRadixString(16).toUpperCase().padLeft(5, '0')})';

packages/flutter/test/widgets/icon_test.dart

@@ -127,6 +127,20 @@ void main() {
     expect(richText.text.style!.fontFamily, equals('Roboto'));
   });
 
+  testWidgets('Icon with custom fontFamilyFallback', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: Icon(IconData(0x41, fontFamilyFallback: <String>['FallbackFont'])),
+        ),
+      ),
+    );
+
+    final RichText richText = tester.firstWidget(find.byType(RichText));
+    expect(richText.text.style!.fontFamilyFallback, equals(<String>['FallbackFont']));
+  });
+
   testWidgets('Icon with semantic label', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);