Fix last row label state after collapse and expand

[tarekquao]

This fixes the issue found in #2368 where in a grouped state (within Datagrid), the last grouped row header seemed as if it had been already unfolded showing the (-) sign instead of the (+) sign.
Now the last grouped row rightly shows the (+) sign.

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[texodus]

You can use View::set_depth for this.

[texodus]

This only checks whether the row is the last row in the viewport, not the dataset. it just makes the last row visible on screen always appear folded.

Screen.Recording.2025-02-09.at.9.03.15.PM.mov

[texodus]

Thanks for the PR, but I don't think this approach is going to work. I can see two potential approaches:

1. Capture an n + 1 sized window in the dataListener, then use this row to determine the collapse state. We'd need to be careful to make sure the extra row doesn't get rendered or we'll end up with the same problem.
2. Add an explcit View API to fetch this data, which is beyond the scope of this comment.