JSON generated from Swift message with >=16 fields exposes `storage` field

Using this protobuf message:

message ManyFields {
  int32 field_1 = 1;
  int32 field_2 = 2;
  int32 field_3 = 3;
  int32 field_4 = 4;
  int32 field_5 = 5;
  int32 field_6 = 6;
  int32 field_7 = 7;
  int32 field_8 = 8;
  int32 field_9 = 9;
  int32 field_10 = 10;
  int32 field_11 = 11;
  int32 field_12 = 12;
  int32 field_13 = 13;
  int32 field_14 = 14;
  int32 field_15 = 15;
  int32 field_16 = 16;
  int32 field_17 = 17;
  int32 field_18 = 18;
}

Then create and object and encode to json (similar than in your JsonLitmusTest.swift):

let manyFieldsWire: ManyFields = ManyFields(
            field_1: 1, field_2: 2, field_3: 3, field_4: 4, field_5: 5, field_6: 6, field_7: 7,
            field_8: 8, field_9: 9, field_10: 10, field_11: 11, field_12: 12, field_13: 13,
            field_14: 14, field_15: 15, field_16: 16, field_17: 17, field_18: 18 )
         // Serialize to JSON
        let manyFieldsJsonWireData = try! JSONEncoder().encode(manyFieldsWire)
        let manyFieldsJsonWire = String(data: manyFieldsJsonWireData, encoding: .utf8)!
        print("manyFields JSON Wire:\n" + manyFieldsJsonWire)
}

Produces the following JSON:

{
  "storage": {
    "field_14": 14,
    "field_5": 5,
    "field_15": 15,
    "field_2": 2,
    "field_7": 7,
    "field_10": 10,
    "field_16": 16,
    "field_4": 4,
    "field_11": 11,
    "field_9": 9,
    "field_17": 17,
    "field_1": 1,
    "field_6": 6,
    "field_12": 12,
    "field_18": 18,
    "field_13": 13,
    "field_3": 3,
    "field_8": 8
  }
}

As you can see there's a top-level storage in the JSON that in my opinion shouldn't be exposed.