Fortran/OpenMP: Fix DT struct-component with 'alloc' and array descr

Fortran/OpenMP: Fix DT struct-component with 'alloc' and array descr

When using 'map(alloc: var, dt%comp)' needs to have a 'to' mapping of
the array descriptor as otherwise the bounds are not available in the
target region. - Likewise for character strings.

This patch implements this; however, some additional issues are exposed
by the testcase; those are '#if 0'ed and will be handled later.

Submitted to mainline (but pending review):
https://gcc.gnu.org/pipermail/gcc-patches/2022-November/604887.html

gcc/fortran/ChangeLog:

	* trans-openmp.cc (gfc_trans_omp_clauses): Ensure DT struct-comp with
	array descriptor and 'alloc:' have the descriptor mapped with 'to:'.

libgomp/ChangeLog:

	* testsuite/libgomp.fortran/target-enter-data-3.f90: New test.