[QNN EP] Initial INT4 support (#21171)
### Description
- Adds support for int4 quantized weights (per-tensor and per-channel)
on QNN EP
- Adds test script that creates an INT4 qdq model with a Conv
- Adds a unit tests demonstrating accuracy issues.
### Motivation and Context
This is the next step in being able to run models that use 4-bit
quantized weights on QNN EP.
