[Triton-MLIR][OPTIMIZER] Cleaned up swizzling (#869)

Swizzling is no longer implemented as a separate pass. It is instead
done in a specialized constructor of SharedEncodingAttr, and tested via
google tests instead of triton-opt + filecheck.

In the future we may want to implement it as a pass again once we have
an additional dialect between TritonGPU and LLVM.

python/triton/compiler.py

@@ -885,7 +885,6 @@ def ttir_to_ttgir(mod, num_warps, num_stages):
     pm.add_coalesce_pass()
     pm.add_triton_gpu_combine_pass()
     pm.add_licm_pass()
-    pm.add_triton_gpu_swizzle_pass()
     pm.add_triton_gpu_combine_pass()
     pm.add_cse_pass()
     pm.run(mod)