[Bug] Align `fromDateTime` arg order to `asDateTime`

[stevebauman]

The argument order for fromDateTime must follow asDateTime in v3:

public function fromDateTime($type, $value)
{
    return (new Timestamp($type))->fromDateTime($value);
}

public function asDateTime($value, $type)
{
    return (new Timestamp($type))->toDateTime($value);
}