When creating new fake methods from functions also initialize their mangled names.

src/Generator/Passes/FunctionToInstanceMethodPass.cs

@@ -44,6 +44,7 @@ namespace CppSharp.Passes
                     Namespace = @class.Namespace,
                     Name = function.Name,
                     OriginalName = function.OriginalName,
+                    Mangled = function.Mangled,
                     Access = AccessSpecifier.Public,
                     Kind = CXXMethodKind.Normal,
                     ReturnType = function.ReturnType,

src/Generator/Passes/FunctionToStaticMethodPass.cs

@@ -35,6 +35,7 @@ namespace CppSharp.Passes
                 Namespace = @class.Namespace,
                 Name = name,
                 OriginalName = function.OriginalName,
+                Mangled = function.Mangled,
                 Access = AccessSpecifier.Public,
                 Kind = CXXMethodKind.Normal,
                 ReturnType = function.ReturnType,