Function prepare_added_attribute 

pub fn prepare_added_attribute(
    types: &dyn FunctionTypeResolver,
    composites: &dyn CompositeTypeCatalog,
    definition: &StoredComposite,
    addition: &CompositeAttributeAddition,
) -> Result<StoredCompositeAttribute, SQLError>

ATExecAddColumn for a composite relation, after its owner and kind have been checked.