[flang][runtime] Finalize polymorphic components using dynamic type (#67040)

Previous code was finalizing polymorphic components according to static
type (calling the static type final routine, if any).

There is no way (I think) to know from a
Fortran::runtime::typeInfo::Component if an allocatable component is
polymorphic or not. So this patch just always uses the dynamic type
descriptor to check for derived type allocatable component finalization.