Fix AOT compilation errors

The problem

Upon compilation the Mono & IL2CPP compilers do their best to figure out which types you are going to use, and IL2CPP even discards the rest (called bytecode stripping). Here lies the issue; for the compilers cannot see the what code is referenced using reflection.

This can lead to errors in the format of:

Newtonsoft.Json.JsonSerializationException : Unable to find a constructor to use for type MyCSharpType. A class should either have a default constructor, one constructor with arguments or a constructor marked with the JsonConstructor attribute. Path 'TheProperty'.

Second example:

ExecutionEngineException: Attempting to call method 'Newtonsoft.Json.Utilities.CollectionWrapper`1[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]::.ctor' for which no ahead of time (AOT) code was generated.

-or, in other (less verbose) words:

Attempting to call constructor of type Newtonsoft.Json.Utilities.CollectionWrapper<int> for which no ahead of time (AOT) code was generated.

The alternatives

There are three main solutions available here. There's no one-shoe-fits-all, so to give a short overview here's a table describing the differences.

Practically speaking you will most probably be using multiple solutions, but I encourage as best practice to use the AotHelper and link.xml solutions more than the Preserve attribute for the reason that you can bundle up the configs into a single file, making it easier to get an overview of your configuration.

Ensure no stripping for ... :	force compilation using the AotHelper	disable bytecode stripping using a link.xml file	disable bytecode stripping using the Preserve attribute
non-generic class	✔	✔	✔
generic class	✔	✔	❌
generic variants (ex: List<MyClass>) that's only referenced via reflection	✔	❌	❌
entire assembly	❌	✔	✔
members (methods, fields, properties)	✔	✔	✔
inaccessible types (ex: private or internal classes/members)	❌	✔	❌
read-only code (ex: precompiled DLLs, or C# source code from UPM packages)	✔	✔	❌
Extra
intellisense support	✔	❌	✔
errors when misconfigured, i.e. known to be correctly configured before trying to run with a full rebuild using IL2CPP	✔	❌	✔
configs for multiple types can be placed in a single file	✔	✔	❌
does not need to reference UnityEngine.dll	✔	✔	✔