[Flang] Enable support for conversion of recursive record types

Uses the recursive type conversion implemented in D113579, D113580.
Tests check for recursive and mutually recursive types.

Note: The downstream implementation for recursive types is a bit old
and is based on a static map. This was removed while upstreaming
(https://reviews.llvm.org/D112961) based on review comments. Since
the recursive type conversion is now available in MLIR we are using
that. If this patch is accepted we can use the same in the downstream
implementation.
Part of upstreaming flang from fir-dev branch of https://github.com/flang-compiler/f18-llvm-project.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D115937



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