Add HLG decoding for streaming CTC models

[csukuangfj]

Usage examples

curl -SL -O https://github.com/k2-fsa/sherpa-onnx/releases/download/asr-models/sherpa-onnx-streaming-zipformer-ctc-small-2024-03-18.tar.bz2
tar xvf sherpa-onnx-streaming-zipformer-ctc-small-2024-03-18.tar.bz2
rm sherpa-onnx-streaming-zipformer-ctc-small-2024-03-18.tar.bz2
repo=sherpa-onnx-streaming-zipformer-ctc-small-2024-03-18

./build/bin/sherpa-onnx \
  --zipformer2-ctc-model=$repo/ctc-epoch-30-avg-3-chunk-16-left-128.int8.onnx \
  --ctc-graph=$repo/HLG.fst \
  --tokens=$repo/tokens.txt \
  $repo/test_wavs/0.wav \
  $repo/test_wavs/1.wav \
  $repo/test_wavs/8k.wav