[QNN EP] Transform SFIXED to UFIXED on InstanceNorm scale (#24952)
### Description- In the InstanceNormOpBuilder, when inputs[1] (scale) is constant and running on NPU backend, transform S8 scale into U8 scale since Qnn Htp does not support SFIXED InstanceNorm scale.
- Allow RunInstanceNormQDQTest to specify different data types for inputs[0] (data) and inputs[1] (scale)
- Add corresponding unit test QnnHTPBackendTests.InstanceNormU8S8
### Motivation and Context
- Prevent InstanceNormOp from fallback to CPU on SFIXED scale