@Index doesn't work for getter/setter properties

[23doors]

Basic info (please complete the following information):

• ObjectBox version: 2.0.0
• Flutter/Dart SDK: [e.g. 2.0.0, or the output of dart --version or flutter --version]
• Null-safety enabled: yes
• Reproducibility: always

Steps to reproduce

Entity with:

  @Transient()
  DateTime? utcDate;

  @Index()
  int get dbUtcDate => utcDate?.millisecondsSinceEpoch ?? 0;

  set dbUtcDate(int value) {
    utcDate = DateTime.fromMillisecondsSinceEpoch(value, isUtc: true);
  }

generates objectbox-model.json without index:

        {
          "id": "46:2219823090073850885",
          "name": "dbUtcDate",
          "type": 6
        }

Expected behavior

Above should generate indexed property, just like this does (version without transient + getter/setter):

  @Index()
  int? dbUtcDate;

generates:

        {
          "id": "46:2219823090073850885",
          "name": "dbUtcDate",
          "type": 6,
          "flags": 8,
          "indexId": "35:4553977394910343818"
        }

[greenrobot-team]

Thanks for reporting! Merging this with #392 (and closing this).