toDuration method
Converts this ISO duration to an approximate Dart duration.
The days
are converted by assuming 365 days per year and 30 days per month: days: years * 365 + months * 30 + weeks * 7 + days
Compare addTo for a better handling of this duration.
Implementation
Duration toDuration() => Duration(
days: years * 365 + months * 30 + weeks * 7 + days,
hours: hours,
minutes: minutes,
seconds: seconds,
);