[MLIR][TORCH] Add OnnxToLinalg lowering pipeline

[vivekkhandelwal1]

This commit adds the lowering pipeline for the onnx-torch IR to linalg-on-tensors backend IR. The pipeline comprises of three stages: 1.) OnnxToTorch Lowering Pass 2.) TorchFunctionToTorchBackend Pipeline 3.) TorchBackendToLinalgOnTensorsBackend Pipeline

Signed-Off By: Vivek Khandelwal [email protected]

[stellaraccident]

What is this doing above and beyond the normal torch to linalg pipeline?

I'd rather just teach that one what to do vs having another bespoke pipeline.

(Or if just adding a pass at the front door onnx, delegate to the regular one)

[vivekkhandelwal1]

This PR is not required anymore therefore closing it.