Add Android demo for speaker recognition (#536)

See pre-built Android APKs at 
https://k2-fsa.github.io/sherpa/onnx/speaker-identification/apk.html

sherpa-onnx/csrc/speaker-embedding-extractor-model.h

@@ -6,6 +6,11 @@
 
 #include <memory>
 
+#if __ANDROID_API__ >= 9
+#include "android/asset_manager.h"
+#include "android/asset_manager_jni.h"
+#endif
+
 #include "onnxruntime_cxx_api.h"  // NOLINT
 #include "sherpa-onnx/csrc/speaker-embedding-extractor-model-meta-data.h"
 #include "sherpa-onnx/csrc/speaker-embedding-extractor.h"
@@ -17,6 +22,11 @@ class SpeakerEmbeddingExtractorModel {
   explicit SpeakerEmbeddingExtractorModel(
       const SpeakerEmbeddingExtractorConfig &config);
 
+#if __ANDROID_API__ >= 9
+  SpeakerEmbeddingExtractorModel(AAssetManager *mgr,
+                                 const SpeakerEmbeddingExtractorConfig &config);
+#endif
+
   ~SpeakerEmbeddingExtractorModel();
 
   const SpeakerEmbeddingExtractorModelMetaData &GetMetaData() const;