We allow mapping dictionaries of simple structs using the default C# serializer. This issue is about doing the same when the struct is used as a simple property. For example:

```
class CustomStructEntity : IdEntity

{   public MonetaryAmount money \{ get; set; }

}

record struct MonetaryAmount

{   public string Currency \{ get; set; }

  public decimal Amount { get; set; }
}
```

Initial place to look: `BsonSerializerFactory.CreateTypeSerializer`