[flang][lowering] Add support for lowering of the `ieor` intrinsic

This patch adds support for lowering of the `ieor` intrinsic from Fortran
to the FIR dialect of MLIR.

This is part of the upstreaming effort from the `fir-dev` branch in [1].

[1] https://github.com/flang-compiler/f18-llvm-project



Co-authored-by: V Donaldson <vdonaldson@nvidia.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: Valentin Clement <clementval@gmail.com>

Differential Revision: https://reviews.llvm.org/D121791