[mlir][scf] Extend consumer fuse to single nested scf.for (llvm#94190)

Refactor current consumer fusion based on `addInitOperandsToLoopNest` to support single nested `scf.for`, E.g.

```
%0 = scf.for() {
  %1 = scf.for() {
     tiledProducer
  }
  yield %1
}
%2 = consumer ins(%0)
```