feat(validation): add to $errors if the validator has $message

[pikax]

fix #493

If a validator has a $message and the validations fails it will be added to the $errors

    const $message = "Invalid value";
    const v = useValidation({
      input: {
        $value: "",
        required: {
          $validator(x: string) {
            return false;
          },
          $message
        }
      },
      otherInput: {
        $value: "",
        required(x: string) {
          return false;
        }
      }
    });

    expect(v.input.$errors).toMatchObject([$message]);
    expect(v.otherInput.$errors).toMatchObject([]);