Generate valid C# for returned const void pointers

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -182,7 +182,14 @@ namespace CppSharp.Generators.CSharp
             }
 
             if (new QualifiedType(pointer, quals).IsConstRefToPrimitive())
+            {
+                if (finalPointee.IsPrimitiveType(PrimitiveType.Void))
+                {
+                    Context.Return.Write($"new {typePrinter.IntPtrType}(*{Context.ReturnVarName})");
+                    return true;
+                }
                 Context.Return.Write("*");
+            }
 
             Context.Return.Write(Context.ReturnVarName);
             return true;

tests/CSharp/CSharp.Tests.cs

@@ -95,7 +95,9 @@ public unsafe class CSharpTests : GeneratorTestFixture
         }
 
         CSharp.CSharp.ReturnCharPointer();
-        CSharp.CSharp.RValueReferenceToPointer(null);
+        int value = 5;
+        IntPtr intPtr = CSharp.CSharp.RValueReferenceToPointer((void**) &value);
+        Assert.That((int) intPtr, Is.EqualTo(value));
 
 #pragma warning restore 0168
 #pragma warning restore 0219

tests/CSharp/CSharp.cpp

@@ -1565,8 +1565,9 @@ const char*& takeConstCharStarRef(const char*& c)
     return c;
 }
 
-void rValueReferenceToPointer(void*&& v)
+const void*& rValueReferenceToPointer(void*&& v)
 {
+    return (const void*&) v;
 }
 
 boolean_t takeTypemapTypedefParam(boolean_t b)

tests/CSharp/CSharp.h

@@ -1307,7 +1307,7 @@ public:
 DLL_API void va_listFunction(va_list v);
 DLL_API char* returnCharPointer();
 DLL_API const char*& takeConstCharStarRef(const char*& c);
-DLL_API void rValueReferenceToPointer(void*&& v);
+DLL_API const void*& rValueReferenceToPointer(void*&& v);
 
 struct {
     struct {