Refactor the JNI interface to make it more modular and maintainable (#802)

kotlin-api-examples/test_tts.kt

@@ -0,0 +1,30 @@
+package com.k2fsa.sherpa.onnx
+
+fun main() {
+  testTts()
+}
+
+fun testTts() {
+  // see https://github.com/k2-fsa/sherpa-onnx/releases/tag/tts-models
+  // https://github.com/k2-fsa/sherpa-onnx/releases/download/tts-models/vits-piper-en_US-amy-low.tar.bz2
+  var config = OfflineTtsConfig(
+    model=OfflineTtsModelConfig(
+      vits=OfflineTtsVitsModelConfig(
+        model="./vits-piper-en_US-amy-low/en_US-amy-low.onnx",
+        tokens="./vits-piper-en_US-amy-low/tokens.txt",
+        dataDir="./vits-piper-en_US-amy-low/espeak-ng-data",
+      ),
+      numThreads=1,
+      debug=true,
+    )
+  )
+  val tts = OfflineTts(config=config)
+  val audio = tts.generateWithCallback(text="“Today as always, men fall into two groups: slaves and free men. Whoever does not have two-thirds of his day for himself, is a slave, whatever he may be: a statesman, a businessman, an official, or a scholar.”", callback=::callback)
+  audio.save(filename="test-en.wav")
+  tts.release()
+  println("Saved to test-en.wav")
+}
+
+fun callback(samples: FloatArray): Unit {
+  println("callback got called with ${samples.size} samples");
+}