[MLIR] [Python] Fixed a long standing bug in the `PyRegionListIterator` (#188475)

`PyRegionIterator` did not account for start index/step, so this commit
removes it in favor of the sequence iterator provided by CPython.

The previous attempt in #137232 bitrotted, so I decided to open a new
PR.

GitOrigin-RevId: 8afb4620d6b6d32341647ed31fa2f4273cff9ca3
3 files changed
tree: 46d17fe4d9de520b9fdd9d404158a422e7290f0c
  1. benchmark/
  2. cmake/
  3. docs/
  4. examples/
  5. include/
  6. lib/
  7. python/
  8. test/
  9. tools/
  10. unittests/
  11. utils/
  12. .clang-format
  13. .clang-tidy
  14. CMakeLists.txt
  15. LICENSE.TXT
  16. Maintainers.md
  17. README.md
README.md

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