[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.
llvm-project
16aa2833 - [MLIR] Refactor the walkAndApplyPatterns driver to remove the recursion (#154037)
