Fix hover tooltip for layout containers

[optozorax]

I have found that ui.horizontal(...).response.on_hover_text(...) doesn't work, although documentation says otherwise:

The returned [Response](https://docs.rs/egui/latest/egui/response/struct.Response.html) will only have checked for mouse hover but can be used for tooltips (on_hover_text). It also contains the [Rect](https://docs.rs/egui/latest/egui/struct.Rect.html) used by the horizontal layout.The returned [Response](https://docs.rs/egui/latest/egui/response/struct.Response.html) will only have checked for mouse hover but can be used for tooltips (on_hover_text). It also contains the [Rect](https://docs.rs/egui/latest/egui/struct.Rect.html) used by the horizontal layout.

So I added fix to this into tooltip, but this looks like a hack, and I don't know a better place to do so. Do you have a better idea?

This PR is split into two commits: first commit adds test, and you can see wrong behaviour in the image. Second commit fixes this and also regenerates the image and you can now see tooltip.

I have used LLM to help me with this PR (codex). And I retained LLM comment, because such hacks should have some comments, and it seems ok to me.

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/7909-reproduce-horizontal-tooltip-regression-from-main
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