Add TTS example for Java API. (#1176)

It plays the generated audio as it is still generating.

sherpa-onnx/java-api/src/com/k2fsa/sherpa/onnx/OfflineTtsCallback.java

@@ -0,0 +1,6 @@
+package com.k2fsa.sherpa.onnx;
+
+@FunctionalInterface
+public interface OfflineTtsCallback {
+    Integer invoke(float[] samples);
+}