Add C API for Kokoro TTS models (#1717)

sherpa-onnx/c-api/cxx-api.h

@@ -338,9 +338,19 @@ struct OfflineTtsMatchaModelConfig {
   float length_scale = 1.0;  // < 1, faster in speed; > 1, slower in speed
 };
 
+struct OfflineTtsKokoroModelConfig {
+  std::string model;
+  std::string voices;
+  std::string tokens;
+  std::string data_dir;
+
+  float length_scale = 1.0;  // < 1, faster in speed; > 1, slower in speed
+};
+
 struct OfflineTtsModelConfig {
   OfflineTtsVitsModelConfig vits;
   OfflineTtsMatchaModelConfig matcha;
+  OfflineTtsKokoroModelConfig kokoro;
   int32_t num_threads = 1;
   bool debug = false;
   std::string provider = "cpu";