ExecutionEngineException in Unity3d IL2CPP iOS

Running code using Infer.NET fails with an ExecutionEngineException on iOS when built with IL2CPP from Unity3d. Some of the instantiations of generic types used internally don't exist during compile time which causes the corresponding iOS AOT code to be missing at runtime.

Details:
Unity 2018.3
Microsoft.ML.Probabilistic.dll
Microsoft.ML.Probabilistic.Compiler.dll

```
ExecutionEngineException: Attempting to call method 'Microsoft.ML.Probabilistic.Models.ModelBuilder::SearchExpression' for which no ahead of time (AOT) code was generated.
at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Utilities.Util.Invoke (System.Reflection.MethodBase method, System.Object target, System.Object[] parameters) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.ModelBuilder.Build (Microsoft.ML.Probabilistic.Models.InferenceEngine engine, System.Boolean inferOnlySpecifiedVars, System.Collections.Generic.IEnumerable`1[T] vars) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.BuildAndCompile (System.Boolean inferOnlySpecifiedVars, System.Collections.Generic.IEnumerable`1[T] vars) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.GetCompiledInferenceAlgorithm (System.Boolean inferOnlySpecifiedVars, Microsoft.ML.Probabilistic.Models.IVariable var) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.Infer (Microsoft.ML.Probabilistic.Models.IVariable var) [0x00000] in <00000000000000000000000000000000>:0
at Main.TwoCoins () [0x00000] in <00000000000000000000000000000000>:0
at Main.Start () [0x00000] in <00000000000000000000000000000000>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Utilities.Util.Invoke (System.Reflection.MethodBase method, System.Object target, System.Object[] parameters) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.ModelBuilder.Build (Microsoft.ML.Probabilistic.Models.InferenceEngine engine, System.Boolean inferOnlySpecifiedVars, System.Collections.Generic.IEnumerable`1[T] vars) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.BuildAndCompile (System.Boolean inferOnlySpecifiedVars, System.Collections.Generic.IEnumerable`1[T] vars) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.GetCompiledInferenceAlgorithm (System.Boolean inferOnlySpecifiedVars, Microsoft.ML.Probabilistic.Models.IVariable var) [0x00000] in <00000000000000000000000000000000>:0
at Microsoft.ML.Probabilistic.Models.InferenceEngine.Infer (Microsoft.ML.Probabilistic.Models.IVariable var) [0x00000] in <00000000000000000000000000000000>:0
at Main.TwoCoins () [0x00000] in <00000000000000000000000000000000>:0
at Main.Start () [0x00000] in <00000000000000000000000000000000>:0

(Filename: currently not available on il2cpp Line: -1)```