[MLIR][python bindings] Fix inferReturnTypes + AttrSizedOperandSegments for optional operands

Right now `inferTypeOpInterface.inferReturnTypes` fails because there's a cast in there to `py::sequence` which throws a `TypeError` when it tries to cast the `None`s. Note `None`s are inserted into `operands` for omitted operands passed to the generated builder:

```
    operands.append(_get_op_result_or_value(start) if start is not None else None)
    operands.append(_get_op_result_or_value(stop) if stop is not None else None)
    operands.append(_get_op_result_or_value(step) if step is not None else None)
```

Note also that skipping appending to the list operands doesn't work either because [[ https://github.com/llvm/llvm-project/blob/27c37327da67020f938aabf0f6405f57d688441e/mlir/lib/Bindings/Python/IRCore.cpp#L1585 | build generic ]] checks against the number of operand segments expected.

Currently the only way around is to handroll through `ir.Operation.create`.

Reviewed By: rkayaith

Differential Revision: https://reviews.llvm.org/D151409