support @JsonEnum(valueField "index", indexOffset: 100)

[RelicOfTesla]

@JsonEnum(valueField: 'index') // already support 
enum some_status_0 {
  aaa,
  bbb,
}

@JsonEnum(valueField: 'index', indexOffset: 100) 
enum some_status_100 {
  aaa,
  bbb,
}

const _$some_status_0 EnumMap = {
  some_status_0.aaa: 0,
  some_status_0.bbb: 1,
};
const _$some_status_100 EnumMap = {
  some_status_100.aaa: 100,
  some_status_100.bbb: 101,
};