Unified OV compile_model API in OVEP (#20700)
### Description
Have a unified API in OVEP that pass the ONNX graph proto from ORT to OV
for compilation
### Motivation and Context
The earlier implementation used two different flows when onnx model path
is present vs model laoded from memory.
The former directly passed the onnx model path to OV when the graph is
fully supported by EP. While the latter pass the ORT model proto to OV.
This cause a difference in results when ORT optimizations are enabled.
This PR address this issue.
