C#: Assume 64-bit types when type has no meta

When the C# bindings generator finds a type without meta assume the type
refers to the 64-bit version of the type:
- `float` is converted to `double`
- `int` is converted to `long`

modules/mono/editor/script_templates/Node/default.cs

@@ -11,7 +11,7 @@ public partial class _CLASS_ : _BASE_
     }
 
     // Called every frame. 'delta' is the elapsed time since the previous frame.
-    public override void _Process(float delta)
+    public override void _Process(double delta)
     {
     }
 }