onnxruntime

Fix EmbedLayerNormalization fusion related to LayerNormalization optional input (#22371)

This fixes a bug found by libfuzzer: 

LayerNormalization third input (beta) is optional. The following code
has potential out of bound access if the input is not available:
```
NodeArg* beta = layer_norm_node.MutableInputDefs()[2];
```

This adds a check to ensure the third input exists before fusion.

[AB#49036](https://aiinfra.visualstudio.com/6a833879-cd9b-44a4-a9de-adc2d818f13c/_workitems/edit/49036)