Fix visual overflow when overscrolling RenderShrinkWrappingViewport

[Piinks]

Fixes #89717 for real this time. :)

#89717 is a regression that was caused by #87143 while resolving #10949
#90419 originally sought to resolve it, but the test cases in that change did not account for every case of visual overflow.

This updates hasVisualOverflow so that the clip is properly applied when overscrolling a shrinkwrapping viewport. Seen here in the golden file test I added.

Because these images are translucent, the images look the same on github in light mode. Switching to dark mode makes the difference clearer.

Overflowing

Not Overflowing 🎉

There are a lot of tests for each of these changes, and so while I was here I cleaned then up a bit to be more organized.

Pre-launch Checklist

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• I listed at least one issue that this PR fixes in the description above.
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• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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[skia-gold]

Gold has detected about 4 new digest(s) on patchset 1.
View them at https://flutter-gold.skia.org/cl/github/91620

[flutter-dashboard]

Golden file changes have been found for this pull request. Click here to view and triage (e.g. because this is an intentional change).

If you are still iterating on this change and are not ready to resolve the images on the Flutter Gold dashboard, consider marking this PR as a draft pull request above. You will still be able to view image results on the dashboard, commenting will be silenced, and the check will not try to resolve itself until marked ready for review.

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Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

Changes reported for pull request #91620 at sha 2850768

[goderbauer]

LGTM

But is there a way to visualize the difference in the golden files better even on white background? Maybe add a solid color dart background around everything? I imagine that this will get confusing again when the golden breaks and we need to debug what's different...

[skia-gold]

Gold has detected about 2 new digest(s) on patchset 2.
View them at https://flutter-gold.skia.org/cl/github/91620

[Piinks]

Fixed the golden files to add more contrast.

[skia-gold]

Gold has detected about 1 new digest(s) on patchset 4.
View them at https://flutter-gold.skia.org/cl/github/91620

[git2321231]

@Piinks Any progress？