Private and firstprivate recipes can now be created and populated
through the createAndPopulate method. The populating of recipe bodies is
done through using the PointerLikeType and MappableType interfaces (with
MappableType support still in progress).
The existing create() API remains available for cases where dialects
need manual recipe population (e.g., for frontend-specific semantics
like default value initialization or constructor calls).
Testing exercises the new API with memref types.
