Resolve feedback about iterator member maps
Reject iterator-dependent derived type member maps for now. These maps
would otherwise bypass the parent/member bookkeeping in processMapObjects,
including parentMemberIndices construction and mapper resolution with
hasParentObj=true.
Without that bookkeeping, lowering map(iterator(...): x%a(i)) could emit
an incomplete parent partial map. Emit a TODO instead of silently generating
incorrect or incomplete mapping IR.
