Add Decimal primitive types to the AST type model.

src/AST/CppTypePrinter.cs

@@ -153,6 +153,19 @@ namespace CppSharp.AST
                         throw new ArgumentOutOfRangeException();
                     }
                 }
+                case PrimitiveType.Decimal:
+                {
+                    switch (PrintFlavorKind)
+                    {
+                    case CppTypePrintFlavorKind.C:
+                    case CppTypePrintFlavorKind.Cpp:
+                        return "_Decimal32";
+                    case CppTypePrintFlavorKind.ObjC:
+                        return "NSDecimalNumber";;
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                    }
+                }
             }
 
             throw new NotSupportedException();

src/AST/Type.cs

@@ -1140,7 +1140,8 @@ namespace CppSharp.AST
         Float128,
         IntPtr,
         UIntPtr,
-        String
+        String,
+        Decimal
     }
 
     /// <summary>