[two_dimensional_scrollables] Fix horizontal scrolled tree view hit testing

[MousyBusiness]

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[gemini-code-assist]

Code Review

This pull request addresses a hit-testing bug in the TreeView widget that occurred when the content was horizontally scrolled. The fix involves changing how the hit-test rectangle for each row is calculated in RenderTreeViewport. Instead of using the viewport's width, it now correctly uses the row's actual width. This ensures that the entire row is interactive, even the parts that are scrolled into view horizontally. The PR also includes the corresponding version bump and an entry in the CHANGELOG.md. The changes are correct, but a test case to cover this fix would be a valuable addition.

[gemini-code-assist]

This change correctly fixes the hit testing issue for horizontally scrolled content. However, there doesn't appear to be a new test case that covers this specific scenario. To prevent regressions, it would be beneficial to add a test that:

1. Creates a TreeView with a row wider than the viewport.
2. Scrolls horizontally to reveal the overflowed part of the row.
3. Taps on the overflowed part and asserts that the tap is correctly handled.

This would ensure the fix is working as expected and remains stable in the future.

References

1. The repository style guide states that code changes should have appropriate tests. ^(link)