[mlir][sparse] recognize ReLu operation during sparsification (#92016)

This is a proof of concept recognition of the most basic forms of ReLu
operations, used to show-case sparsification of end-to-end PyTorch
models. In the long run, we must avoid lowering such constructs too
early (with this need for raising them back).

See discussion at

https://discourse.llvm.org/t/min-max-abs-relu-recognition-starter-project/78918