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

<!--
Please read the "Making a PR" section of
[`CONTRIBUTING.md`](https://github.com/emilk/egui/blob/master/CONTRIBUTING.md)
before opening a Pull Request!

* Keep your PR:s small and focused.
* The PR title is what ends up in the changelog, so make it descriptive!
* If applicable, add a screenshot or gif.
* If it is a non-trivial addition, consider adding a demo for it to
`egui_demo_lib`, or a new example.
* Do NOT open PR:s from your `master` branch, as that makes it hard for
maintainers to test and add commits to your PR.
* Remember to run `cargo fmt` and `cargo clippy`.
* Open the PR as a draft until you have self-reviewed it and run
`./scripts/check.sh`.
* When you have addressed a PR comment, mark it as resolved.

Please be patient! I will review your PR, but my time is limited!
-->

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;