[mlir][TilingInterface] Modify `TilingInterface` methods to better return the...

[mlir][TilingInterface] Modify `TilingInterface` methods to better return the state of the transformed IR.

Currently the `getTiledImplementation` and `generateResultTileValue`
return just `SmallVector<Operation *>` and `FailureOr<Value>`.

- For `getTiledImplementation` returning empty implies tiling wasnt
  done. There is also an implicit assumption that the tiled operation
  results correspond to the tiled values of the result of the original
  operation. This cannot handle cases where the tiled implementation
  might use multiple operations to compute the tiled value for the
  results of the untiled operation. Sometimes, the tiled operation
  might not directly give the tiled values, and might require casts,
  etc to get a replacement.
- For `generateResultTileValue`, it is assumed that the op defining
  the returned `Value` is the operation that represents the tiled
  computation. Again presence of casts, etc violate this.

Instead make these methods return
```
struct TilingResult {
  SmallVector<Operation *> tiledOps;
  SmallVector<Value> tiledValues;
};
```

The `tiledOps` represent the operations generated that are relevant
for subsequent transformations. The `tiledValues` represent the tiled
values for the results of the original operation. This better
transmits the state of the transformed IR.

As a consequence the following methods also return `FailureOr<TilingResult>`
- `tensor::replaceExtractSliceWithTiledProducer`
- `tensor::bubbleUpPadSlice`

Differential Revision: https://reviews.llvm.org/D145133