Add missing tests for ASTNodeBuiltinFunctionExpressionBuilder

Also remove the treatment of tuple of function arguments, since this kind of argument cannot be defined in the language (by now?).

src/language/ast/ASTNodeDataTypeFlattener.cpp

@@ -40,9 +40,11 @@ ASTNodeDataTypeFlattener::ASTNodeDataTypeFlattener(ASTNode& node, FlattenedDataT
               {ASTNodeDataType::build<ASTNodeDataType::type_id_t>(image_sub_domain->m_data_type.nameOfTypeId()), node});
             break;
           }
+            // LCOV_EXCL_START
           default: {
             throw UnexpectedError("invalid data type");
           }
+            // LCOV_EXCL_STOP
           }
         }
         break;