[flang][hlfir] add support for elemental intrinsics with custom handling

Only minimal argument processing is needed here because they will be
lowered properly either by the elemental intrinsic call builder or the
lowering of the scalar call inside the elemental kernel.

Dynamically optional arrays are coming in the next patch.

Depends On: D155291

Differential Revision: https://reviews.llvm.org/D155292