[MLIR] Refactor the walkAndApplyPatterns driver to remove the recursion (#154037)

This is in preparation of a follow-up change to stop traversing
unreachable blocks.

This is not NFC because of a subtlety of the early_inc. On a test case
like:

```
  scf.if %cond {
    "test.move_after_parent_op"() ({
      "test.any_attr_of_i32_str"() {attr = 0 : i32} : () -> ()
    }) : () -> ()
  }
```

We recursively traverse the nested regions, and process an op when the
region is done (post-order).
We need to pre-increment the iterator before processing an operation in
case it gets deleted. However
we can do this before or after processing the nested region. This
implementation does the latter.

0 files changed, 0 insertions, 0 deletions