compiler: Add layout debug info to all nodes when lowering layouts

This enables us to find all layouts e.g. in

```slint
component MyLayout inherits GridLayout { @children }

component FooBar {
   my-layout := MyLayout {
      Rectangle {
      }
   }
}
```

internal/compiler/passes/lower_layout.rs

@@ -246,8 +246,8 @@ fn lower_grid_layout(
     );
     grid_layout_element.borrow_mut().layout_info_prop =
         Some((layout_info_prop_h, layout_info_prop_v));
-    if let Some(d) = grid_layout_element.borrow_mut().debug.last_mut() {
-        d.1 = Some(Layout::GridLayout(grid));
+    for d in grid_layout_element.borrow_mut().debug.iter_mut() {
+        d.1 = Some(Layout::GridLayout(grid.clone()));
     }
 }
 
@@ -436,8 +436,8 @@ fn lower_box_layout(
         .into(),
     );
     layout_element.borrow_mut().layout_info_prop = Some((layout_info_prop_h, layout_info_prop_v));
-    if let Some(d) = layout_element.borrow_mut().debug.last_mut() {
-        d.1 = Some(Layout::BoxLayout(layout));
+    for d in layout_element.borrow_mut().debug.iter_mut() {
+        d.1 = Some(Layout::BoxLayout(layout.clone()));
     }
 }
 
@@ -649,8 +649,8 @@ fn lower_dialog_layout(
         .into(),
     );
     dialog_element.borrow_mut().layout_info_prop = Some((layout_info_prop_h, layout_info_prop_v));
-    if let Some(d) = dialog_element.borrow_mut().debug.last_mut() {
-        d.1 = Some(Layout::GridLayout(grid));
+    for d in dialog_element.borrow_mut().debug.iter_mut() {
+        d.1 = Some(Layout::GridLayout(grid.clone()));
     }
 }