Add WhereDummyDq Transformer to form Node Unit (#25576)
### Description
- Add a GraphTransformer `WhereDummyDq` to insert dummy DequantizeLinear on Where node's initializer input to form a Node Unit when Where node has one DQ and one scalar initializer input
- Add corresponding unit test for the optimization
### Motivation and Context
- To reduce the additional Dequantize and Quantize nodes, we would like to pass `WhereNodeGroupSelector::Check`.
