[User reported] On-device inspector doesn't always select a widget in an overlay

This is a user-reported issue from the 2025 DevTools user survey.

A couple users reported that the on-device inspector doesn’t always select a widget in an overlay.

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### Details:

Currently widget inspection does not work very well for cases such as overlays. The inspector is currently relying on a RenderObject’s hitTest, which doesn’t work for all cases.

It’s also difficult to figure out where to click in order to actually select a widget.

**A few ideas for how this might be improved:**
* Show bounding boxes on hover (see https://github.com/flutter/devtools/issues/7762)
* Along with hitTest, add a hitDebug method to some RenderObjects that would be used instead.
* If a hit test matches multiple routes, then choose the top one.
* Tie each pixel to a single RenderObject
* By default, only select widgets in a user’s project (implemented in https://github.com/flutter/flutter/pull/176530)

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Related issue: https://github.com/flutter/devtools/issues/4869