or function
Passes the test if either of the Validators are valid, and fails if both are invalid
Implementation
Validator or(Validator validator1, Validator validator2) {
return (value) {
final res1 = validator1(value);
final res2 = validator2(value);
return Result(
isValid: res1.isValid || res2.isValid,
expected: '${res1.expected} or ${res2.expected}',
value: value,
);
};
}