[flang] Make sure that conversions are applied in FORALL degenerate contexts

[flang] Make sure that conversions are applied in FORALL degenerate contexts

For the rapid triage push, just add a TODO for the degenerate POINTER
assignment case. The LHD ought to be a variable of type !fir.box, but it
is currently returning a shadow variable for the raw data pointer. More
investigation is needed there.
Make sure that conversions are applied in FORALL degenerate contexts.

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

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D128724

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