[flang][NFC] Add IO lowering tests

These tests were left behind or only partially upstreamed during
the lower code upstreaming.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D128634



Co-authored-by: Kiran Chandramohan <kiran.chandramohan@arm.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>