Use C# Dll in Java Android Project

I would like to use a C# DLL in an Android Project that is developing by Java (Not Xamarin or Mono). My first strategy to solve this contains these steps:

1. Create a C++ usable DLL by DllExport from the C# code. (create a C++ wrapper for C# code)
2. Create a .so library from the C++ project that uses generated DLL from the previous step.

So I've used the DLLExport (https://github.com/3F/DllExport)

C# Side:

namespace NumbersLibCS
{
    public class Math
    {
        public Math()
        {

        }


        [DllExport]
        public static int GetRandomEvenNumber()
        {
            var rnd = new Random();
            int n = rnd.Next(1, 1000 ) * 2;
            return n;
        }
    }
}

But in C++ to use the generated DLL I think I should use just windows.h library that is not available on the Android OS:

#include <windows.h>

typedef int(__cdecl *GetRandomEvenNumber)();
int main(){
 HMODULE lib = LoadLibrary("mycsharp.dll");
 auto getRndNumber= (GetRandomEvenNumber)GetProcAddress(lib, "GetRandomEvenNumber");
 int c = getRndNumber();
}

Now here are my questions:

1. How can I use DLLExport generated DLL without windows.h?
2. Can I use .NetCore 2.0 to achieve this without using DLLExport?