Steps to reproduce:
1. Download attached project
2. Make sure that Manage Stripping level is set to Medium or High
3. Build for Standalone (IL2CPP or Mono)
4. Observe error in the console result in a failed build

Results: Build fails

Reproduced with: 2020.1.0a2, 2019.3.0b2, 2019.2.3f1, 2019.4.9f1

Note:
In TestScript.cs, EnumPolicy is included within the [JsonConverter] attribute.
Without EnumPolicy, the build will succeed (JsonConverter seems to be marked to be preserved), but with it, it will fail.
[PreserveAttribute] on EnumPolicy will fix the issue, however, the linker should be able to preserve types within preserved attributes.