Fix all instances of 4244 and 4267 warnings in OV EP code (#23567)
### Description
Remove MSVC warnings 4244, 4267 from the list of disabled warnings in
cmake.
Fix the code that generates the warnings so that it no longer does.
### Motivation and Context
This makes onnxruntime_providers_openvino.dll pass BinSkim analysis.
Without this change BinSkim complains about the disabled warnings.