[Quant Tool] Update QDQ Pad, Slice, Softmax (#22676)
### Description
Updates python quantization tool:
- Ensures QDQ Pad has equal quantization parameters across input and
output for certain Pad configurations.
- Ensures QDQ Slice always has equal quantization parameters across
input and output.
- Fixes bug when Softmax is _excluded_ from quantization.
### Motivation and Context
QDQ Pad and Slice have lower latency on QNN EP when their quantization
parameters are equal.
