TWO_LETTER_ISO_8601_TIME_ZONE_FORMAT constant
here the ZoneOffset is managed manually to add the colon(:) between two digit hours and two digit minutes
Implementation
static const List<String> TWO_LETTER_ISO_8601_TIME_ZONE_FORMAT = [
'yyyy',
'-',
'mm',
'-',
'dd',
'T',
'HH',
':',
'nn',
':',
'ss',
'.',
'SSS',
'z'
];