onnxruntime

[QNN EP] Apply workaround for Conv validation bug when bias input is implicit (#21764)

### Description
- Adds a dummy bias of all zeros when translating a Conv without an
explicit bias input. This is a workaround for a QNN validation issue
that fails when the optional bias input is not provided.
- Corrects logic for unpacking of **non-zero int4** zero-points. Bug
does not impact models because we currently only support int4
zero-points equal to 0 (symmetric quant). But this would become an issue
in the future if/when QNN supports non-zero int4 zero-points (so good to
fix now).



### Motivation and Context
Support Conv operators without a bias input on QNN EP with the latest
QNN SDK.