[charithaintc]

This PR adds the horizontal fusion capability to matmul and grouped matmul ops. Horizontal fusion is decoupled from tiling and fusion passes, instead it happens at Linalg op level. Eg: Two linalg.matmul ops sharing an input will be fused to a linalg.generic with two outputs.

Here is a summary of main changes.

1. Update decomposition pass to decompose fused matmul generics and fused grouped matmul generics to individual matmuls.
2. Update grouped matmul op defn to support fused form (multi-input multi-output groped matmul)
3. Updated tiling to support fused generic form.
4. Add horizontal fusion pass that runs before tiling and fusion.

Assisted by: Codex, Claude