[VitisAI] 1. api compatbile 2. dynamic load onnx (#18470)
### Description
<!-- Describe your changes. -->
1. Add a backward-compatible API for compiling model.
2. Run-time load vitisai-ep.dll
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
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Co-authored-by: Yueqing Zhang <yueqingz@amd.com>
Co-authored-by: Zhenze Wang <zhenzew@xilinx.com>
