[mlir][linalg] Add output tensor args folding for linalg.tiled_loop.

[mlir][linalg] Add output tensor args folding for linalg.tiled_loop.

Folds away TiledLoopOp output tensors when the following conditions are met:
* result of `linalg.tiled_loop` has no uses
* output tensor is the argument of `linalg.yield`

Example:

```
%0 = linalg.tiled_loop ...  outs (%out, %out_buf:tensor<...>, memref<...>) {
  ...
  linalg.yield %out : tensor ...
}
```

Becomes

```
linalg.tiled_loop ...  outs (%out_buf:memref<...>) {
  ...
  linalg.yield
}
```

Differential Revision: https://reviews.llvm.org/D99333