Fixed duplicated vtable delegate generation by changing the way the unique name is generated.

Previously, we could get duplicated names due to different named methods (setFoo and setFoo1) having overloads (and names for them would be setFoo11 [id: 11] and setFoo11 [id: 1]).

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -2302,7 +2302,7 @@ namespace CppSharp.Generators.CSharp
             var index = overloads.IndexOf(function);
 
             if (index >= 0)
-                identifier += index.ToString(CultureInfo.InvariantCulture);
+                identifier += "_" + index.ToString(CultureInfo.InvariantCulture);
 
             return identifier;
         }