[ORTModule] ATen Support for torch.nn.GroupNorm (#13293)
Model [huggingface's diffusers
library](https://github.com/huggingface/diffusers) has
torch.nn.GroupNorm which will be exported to sub-graph containing ONNX's
InstanceNormalization, which is lack of gradient. The implementation of
ORT's InstanceNormalization will call cuDNN's BatchNorm for part of
computation, which is not efficient compared to PyTorch's
implementation. This PR is to use ATen fallback to support this torch
module, including its forward and backward.
