[webgpu] Fix BatchNormalization ShapeInferenceError for 2D inputs (#26659)
### Description
Test model (happens with any 2D inputs):
[2191__visual_projection_visual_projection.1_BatchNormalization.onnx.zip](https://github.com/user-attachments/files/23758390/2191__visual_projection_visual_projection.1_BatchNormalization.onnx.zip)
Command:
```
python -c "import onnxruntime as ort; ort.InferenceSession('2191__visual_projection_visual_projection.1_BatchNormalization.onnx', providers=['WebGpuExecutionProvider'])"
```
Before (failure):
```
Op (BatchNormalization) [ShapeInferenceError] Tensor must have at least 3 dimensions to convert between channels first and channels last.
```
After (success):
```
(nothing, meaning success)
```
### Motivation and Context
This fixes BatchNormalization on WebGPU, matching CPU version.
cc @guschmue