removeFieldFromGroup method
Implementation
void removeFieldFromGroup(String groupId, String fieldId) {
_update((v) => v.copyWith(
groups: v.groups.map((g) {
if (g.id != groupId) return g;
return g.copyWith(
fields: g.fields.where((f) => f.id != fieldId).toList(),
);
}).toList(),
));
}