[flang] Lower of elemental calls in array expression

This patch adds tests and missing lowering
code to lower elemental function/subroutine calls
in array expression

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

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D121474



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