Convert MIGX IR to ONNX

[causten]

Desciption

As a MIGraphX performance developer I want to break down models in to fused portions and run the single fusion in isolation using different graph optimizers.

Now that the MIGX IR can be extracted in to files PR (#3550) , the next step is to convert the IR back to ONNX. This is very important as it allows for the performance comparison with other ONNX accepting optimizers. Comparing MIGX on a per ONNX operator basis is not as interesting as comparing on a per fusion basis

The ONNX community should have tools to build an ONNX model that will likely come in handy.
It may become easier to create a MIGX api to generate the ONNX Operators but feel free to use the newly generated mlir solutions as your starting point.

Success

Convert each .mlir file to ONNX and run perf results for both migraphx-driver and trtexec

[thenightterorx]

Would this allow models to work with something like deepcache?