Add Dart API for streaming ASR (#933)

sherpa-onnx/flutter/example/lib/streaming_transducer_asr_test.dart

@@ -0,0 +1,61 @@
+// Copyright (c)  2024  Xiaomi Corporation
+import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
+import 'package:flutter/services.dart' show rootBundle;
+import 'dart:typed_data';
+import "dart:io";
+
+import 'package:sherpa_onnx/sherpa_onnx.dart' as sherpa_onnx;
+import './utils.dart';
+
+Future<void> testStreamingTransducerAsr() async {
+  var encoder =
+      'assets/sherpa-onnx-streaming-zipformer-bilingual-zh-en-2023-02-20/encoder-epoch-99-avg-1.int8.onnx';
+  var decoder =
+      'assets/sherpa-onnx-streaming-zipformer-bilingual-zh-en-2023-02-20/decoder-epoch-99-avg-1.onnx';
+  var joiner =
+      'assets/sherpa-onnx-streaming-zipformer-bilingual-zh-en-2023-02-20/joiner-epoch-99-avg-1.int8.onnx';
+  var tokens =
+      'assets/sherpa-onnx-streaming-zipformer-bilingual-zh-en-2023-02-20/tokens.txt';
+
+  var testWave =
+      'assets/sherpa-onnx-streaming-zipformer-bilingual-zh-en-2023-02-20/test_wavs/0.wav';
+
+  encoder = await copyAssetFile(src: encoder, dst: 'encoder.onnx');
+  decoder = await copyAssetFile(src: decoder, dst: 'decoder.onnx');
+  joiner = await copyAssetFile(src: joiner, dst: 'joiner.onnx');
+  tokens = await copyAssetFile(src: tokens, dst: 'tokens.txt');
+  testWave = await copyAssetFile(src: testWave, dst: 'test.wav');
+
+  final transducer = sherpa_onnx.OnlineTransducerModelConfig(
+    encoder: encoder,
+    decoder: decoder,
+    joiner: joiner,
+  );
+
+  final modelConfig = sherpa_onnx.OnlineModelConfig(
+    transducer: transducer,
+    tokens: tokens,
+    modelType: 'zipformer',
+  );
+
+  final config = sherpa_onnx.OnlineRecognizerConfig(model: modelConfig);
+  print(config);
+  final recognizer = sherpa_onnx.OnlineRecognizer(config);
+
+  final waveData = sherpa_onnx.readWave(testWave);
+  final stream = recognizer.createStream();
+
+  stream.acceptWaveform(
+      samples: waveData.samples, sampleRate: waveData.sampleRate);
+  while (recognizer.isReady(stream)) {
+    recognizer.decode(stream);
+  }
+
+  final result = recognizer.getResult(stream);
+  print('result is: ${result}');
+
+  print('recognizer: ${recognizer.ptr}');
+  stream.free();
+  recognizer.free();
+}