Fix: Sides did not apply the layout position correctly. (emilk#5232)

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Run this code

```rs
        CentralPanel::default().show(ctx, |ui| {
            Sides::new().show(
                ui,
                |ui| {
                    ui.label("1");
                },
                |ui| {
                    ui.label("2");
                },
            );
            Sides::new().show(
                ui,
                |ui| {
                    ui.label("11");
                },
                |ui| {
                    ui.label("22");
                },
            );
            Sides::new().show(
                ui,
                |ui| {
                    ui.label("111");
                },
                |ui| {
                    ui.label("222");
                },
            );
        });
```

Before


![before](https://github.com/user-attachments/assets/2678f937-859e-422a-9171-5f2a63166c8f)

After


![after](https://github.com/user-attachments/assets/879892f1-a69d-4540-8e56-8b2448e939ed)

crates/egui/src/containers/sides.rs

@@ -78,7 +78,7 @@ impl Sides {
         let height = height.unwrap_or_else(|| ui.spacing().interact_size.y);
         let spacing = spacing.unwrap_or_else(|| ui.spacing().item_spacing.x);
 
-        let mut top_rect = ui.max_rect();
+        let mut top_rect = ui.cursor();
         top_rect.max.y = top_rect.min.y + height;
 
         let result_left;