This commit adds support for MPNet based models.
MPNet models differ from BERT style models in that:
- Special tokens are different
- Input to the model doesn't require token positions.
To configure an MPNet tokenizer for your pytorch MPNet based model:
```
"tokenization": {
"mpnet": {...}
}
```
The options provided to `mpnet` are the same as the previously supported `bert` configuration.
This improves reporting of trained model size in the response of the stats API.
In particular, it removes the `model_size_bytes` from the `deployment_stats` section and
replaces it with a top-level `model_size_stats` object that contains:
- `model_size_bytes`: the actual model size
- `required_native_memory_bytes`: the amount of memory required to load a model
In addition, these are now reported for PyTorch models regardless of their deployment state.
