Layout Explorer should maintain aspect ratio

STEPS TO REPRODUCE
1. Create a new app using the "skeleton" template.
2. Run it.
3. In the widget inspector, click on one of the ListTiles.

EXPECTED RESULTS
I would have expected to see a horizontal rectangle, with the aspect ratio of the list tile.

ACTUAL RESULTS
The visualization is sized to fit the screen, so even though it is labeled as "h=56" and "w=411.4", the box is actually taller than it is wide.

This gets worse e.g. when you tap the CircleAvatar widget, which is square (actually circular) in the real rendering, but appears like a vertical box in the widget inspector.

I think that, within reason, the aspect ratio of the child being displayed in the widget inspector should match the real aspect ratio. That would help orient the developer.

使用 "skeleton" 模板创建一个新应用来重现该问题，然后为一个 ListTile 和 CircleAvatar 打开 widget inspector 和 Layout Explorer。从该入口点追踪 Layout Explorer 的渲染；当显示的子项在可用屏幕空间内保持其真实宽高比时，即表示完成。

由索引模型根据 Issue 内容生成。