RFR: 8356770: TreeTableView not updated after removing a TreeItem with children and adding it to another parent [v3]

[Andy Goryachev]

On Fri, 14 Nov 2025 15:56:07 GMT, Ziad El Midaoui <zelmidaoui at openjdk.org> wrote:

>> When a subtree is moved in a `TreeTableView` , the visuals don’t update until a resize or expand/collapse. The `TreeTableViewSkin` only rebuilds cells when the expanded row count changes.
>> This PR makes the skin to detect structural changes on `childrenModificationEvent` using new variable `treeStructureDirty`, and in `updateItemCount()` call `requestRebuildCells()` to refresh the visuals.
>
> Ziad El Midaoui has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Minor test changes

Marked as reviewed by angorya (Reviewer).

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PR Review: https://git.openjdk.org/jfx/pull/1971#pullrequestreview-3465982231