function is_non_coercive_operator(operator) {
	return ['=', '||=', '&&=', '??='].includes(operator);
}
Determines whether the value will be coerced on assignment (as with e.g. `+=`).
If not, we may need to proxify the value, or warn that the value will not be
proxified in time
@param {AssignmentOperator} operator