Add comments to functions that iterate over surfaces

These should be kept in sync with `render_input_order_internal`.

src/shell/focus/order.rs

@@ -77,6 +77,8 @@ fn render_input_order_internal<R: 'static>(
     element_filter: ElementFilter,
     mut callback: impl FnMut(Stage) -> ControlFlow<Result<R, OutputNoMode>, ()>,
 ) -> ControlFlow<Result<R, OutputNoMode>, ()> {
+    // NOTE: Keep in sync with other surface iteration functions
+
     if shell
         .zoom_state
         .as_ref()

src/shell/mod.rs

@@ -2046,6 +2046,8 @@ impl Shell {
     }
 
     pub fn visible_output_for_surface(&self, surface: &WlSurface) -> Option<&Output> {
+        // NOTE: Keep in sync with surface iteration in `render_input_order_internal`
+
         if let Some(session_lock) = &self.session_lock {
             return session_lock
                 .surfaces