Contributes to dotnet#107999.

We want _some_ caching. It's unclear what the right caching is (the caching on CoreCLR VM side is [wild](dotnet#107999 (comment))), but given that we sometimes might need to purge caches to avoid turning them into memory leaks, I think the only conclusion is that whoever implements things like:

```csharp
class Dyn : IDynamicInterfaceCastable
{
    public Type InterfaceType { get; init; }
    public Type ImplType { get; init; }

    public RuntimeTypeHandle GetInterfaceImplementation(RuntimeTypeHandle interfaceType)
        => interfaceType.Equals(InterfaceType.TypeHandle) ? ImplType.TypeHandle : throw new Exception();
    public bool IsInterfaceImplemented(RuntimeTypeHandle interfaceType, bool throwIfNotImplemented)
        => interfaceType.Equals(InterfaceType.TypeHandle) ? true : (throwIfNotImplemented ? throw new InvalidCastException() : false);
}
```

Should feel bad, and we don't support their use case.