[fir] Add fir.save_result op

Add the fir.save_result operation. It is use to save an
array, box, or record function result SSA-value to a memory location

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D110407



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