[torch-mlir] provide FX traced graph importer for sparse tensors

[aartbik]

Note that we are waiting for actual FX traced graph support for sparse tensors. For details see

pytorch/pytorch#117188

Until then, however, we provide this clever importer that builds the FX traced graph for for the dense case and then puts a sparse annotation back on the parameters.

With import test.

[stellaraccident]

I wasn't quite ready to accept contributions to this part yet. Let me synchronize the downstream fork tomorrow and make sure we don't get into a merge conflict.

[aartbik]

I wasn't quite ready to accept contributions to this part yet. Let me synchronize the downstream fork tomorrow and make sure we don't get into a merge conflict.

I suspect conflicts will be very light, since I am only touching a few tensor type building parts. But let me know when you are ready.

[stellaraccident]

Should be fine but I'm just trying to juggle less. I'm juggling a downstream pr and almost have the spice flowing to not need the fork. Give me a few hours

[aartbik]

Should be fine but I'm just trying to juggle less. I'm juggling a downstream pr and almost have the spice flowing to not need the fork. Give me a few hours

Of course. Take your time! Just reply here when you are comfortable moving forward.

[stellaraccident]

I've gone ahead and taken steps to unfork the code from the downstream (iree-org/iree#16276). Will take a release cycle to percolate but in the meantime, we're fine with this minor difference.

[aartbik]

Thanks for your flexibility moving this forward quickly!