lessThanDecString method
Relational less than operator. 判断a是否小于b
Implementation
bool lessThanDecString(String a, String b) {
final aDecimal = _safeParseDecimal(a);
final bDecimal = _safeParseDecimal(b);
if (aDecimal == null || bDecimal == null) return false;
return aDecimal < bDecimal;
}