[flang][NFC] Add embox test with character

This test is added to check for multidimensional descriptor of array
substring/derived type component array.

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

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D128990



Co-authored-by: Jean Perier <jperier@nvidia.com>