Add Dart API for homophone replacer (#2167)

flutter/sherpa_onnx/lib/src/homophone_replacer_config.dart

@@ -0,0 +1,29 @@
+// Copyright (c)  2025  Xiaomi Corporation
+
+class HomophoneReplacerConfig {
+  const HomophoneReplacerConfig(
+      {this.dictDir = '', this.lexicon = '', this.ruleFsts = ''});
+
+  factory HomophoneReplacerConfig.fromJson(Map<String, dynamic> json) {
+    return HomophoneReplacerConfig(
+      dictDir: json['dictDir'] as String? ?? '',
+      lexicon: json['lexicon'] as String? ?? '',
+      ruleFsts: json['ruleFsts'] as String? ?? '',
+    );
+  }
+
+  @override
+  String toString() {
+    return 'HomophoneReplacerConfig(dictDir: $dictDir, lexicon: $lexicon, ruleFsts: $ruleFsts)';
+  }
+
+  Map<String, dynamic> toJson() => {
+        'dictDir': dictDir,
+        'lexicon': lexicon,
+        'ruleFsts': ruleFsts,
+      };
+
+  final String dictDir;
+  final String lexicon;
+  final String ruleFsts;
+}