[NFC][Flang] Add simd collapse test case

Flang supports lowering collapse clause to MLIR for worksharing loops
and simd loops. Simd collapse clause is represented in MLIR code as a
simd-loop having a list of indices, bounds and steps where the size of the list
is equal to the collapse value.

Support for simd collapse clause was added by several patches:
https://reviews.llvm.org/D118065 -> basic support for simd-loop in MLIR.
                                    Loop collapsing is done in the same way as
                                    for worksharing loops:
                                    https://reviews.llvm.org/D105706
https://reviews.llvm.org/D125282 -> support for lowering simd clause from
                                    Fortran into MLIR
https://reviews.llvm.org/D125302 -> lowering collapse clause from Fortran to
                                    MLIR. Lowering collapse clause is done
                                    before simd-specific function is called.
https://reviews.llvm.org/D128338 -> modified the MLIR representation of
                                    collapse clause. Removed collapse keyword
                                    in OpenMP MLIR dialect. Use loop list to
                                    represent collapse clause. This loop list
                                    is created by changes from patch:
                                    https://reviews.llvm.org/D125302 and it is
                                    passed to function responsible for lowering
                                    of simd directive which was implemented in
                                    patch: https://reviews.llvm.org/D125282

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D132023



Signed-off-by: Dominik Adamski <dominik.adamski@amd.com>