Add vad clear api for better performance (#366)

* Add vad clear api for better performance

* rename to make naming consistent and remove macro

* Fix linker error

* Fix Vad.kt

android/SherpaOnnxVad/app/src/main/java/com/k2fsa/sherpa/onnx/MainActivity.kt

@@ -161,9 +161,9 @@ class MainActivity : AppCompatActivity() {
                 val samples = FloatArray(ret) { buffer[it] / 32768.0f }
 
                 vad.acceptWaveform(samples)
-                while(!vad.empty()) {vad.pop();}
 
                 val isSpeechDetected = vad.isSpeechDetected()
+                vad.clear()
 
                 runOnUiThread {
                     onVad(isSpeechDetected)

android/SherpaOnnxVad/app/src/main/java/com/k2fsa/sherpa/onnx/Vad.kt

@@ -46,6 +46,8 @@ class Vad(
     // [start: Int, samples: FloatArray]
     fun front() = front(ptr)
 
+    fun clear() = clear(ptr)
+
     fun isSpeechDetected(): Boolean = isSpeechDetected(ptr)
 
     fun reset() = reset(ptr)
@@ -64,6 +66,7 @@ class Vad(
     private external fun acceptWaveform(ptr: Long, samples: FloatArray)
     private external fun empty(ptr: Long): Boolean
     private external fun pop(ptr: Long)
+    private external fun clear(ptr: Long)
     private external fun front(ptr: Long): Array<Any>
     private external fun isSpeechDetected(ptr: Long): Boolean
     private external fun reset(ptr: Long)