modifyAll method
Applies modifiers that alters the date and/or time.
The modifiers are applied in sequence from left to right.
For a list of modifiers and how they behave, see the docs on
DateTimeModifier factories.
Implementation
Expression<DateTime> modifyAll(Iterable<DateTimeModifier> modifiers) {
  return _DependingOnDateTimeExpression(
    forTimestamps: FunctionCallExpression('unixepoch',
        [this, const DateTimeModifier._unixEpoch(), ...modifiers]),
    forIsoString: FunctionCallExpression('datetime', [this, ...modifiers]),
  );
}