GitLab

1. Override the return type so that Sphinx shows the exported symbols.
   (output model types and input torch.nn.Module)
2. Tweak docs for Tacotron2TTSBundle interfaces
3. Fix for HUBERT_ASR_XLARGE

Future work items:
- length computation of GriffinLim
- better way to make InverseMelScale work in inference_mode

- Move wav2vec2 pretrained weights to `torchaudio.pipelines` namespace to align with #1872.
- Split `Wav2Vec2PretrainedModelBundle` into `Wav2Vec2Bundle` (for pre-training model) and  `Wav2Vec2ASRBundle` (for models fine-tuned for ASR).
- Update base URL