Add C++ runtime for Matcha-TTS (#1627)

sherpa-onnx/csrc/offline-tts-impl.h

@@ -7,6 +7,7 @@
 
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "sherpa-onnx/csrc/offline-tts.h"
 
@@ -32,6 +33,9 @@ class OfflineTtsImpl {
   // Number of supported speakers.
   // If it supports only a single speaker, then it return 0 or 1.
   virtual int32_t NumSpeakers() const = 0;
+
+  std::vector<int64_t> AddBlank(const std::vector<int64_t> &x,
+                                int32_t blank_id = 0) const;
 };
 
 }  // namespace sherpa_onnx