fix: detect cyclic references in TreeData.setParent() (#23401) (CP: 24.9)

[vaadin-bot]

This PR cherry-picks changes from the original PR #23401 to branch 24.9.

Original PR description

Previously, TreeData.setParent() only checked for direct self-parenting (item.equals(parent)) but did not detect transitive cycles where a descendant becomes an ancestor. This could corrupt the tree structure, for example when drag-and-drop in TreeGrid moved a parent node under one of its descendants.

Added isAncestorOf() helper method that walks up the ancestor chain to detect if the item being moved is an ancestor of the proposed new parent. If so, setParent() now throws IllegalArgumentException with a clear error message.

The cycle check has O(h) complexity where h is the tree height, which is acceptable for typical tree operations.

Fixes #19337

[vaadin-bot]

This PR is eligible for auto-merging policy, so it has been approved automatically. If there are pending conditions, auto merge (with 'squash' method) has been enabled for this PR[Message is sent from bot]

[sonarqubecloud]

Quality Gate passed

Issues
18 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

1 272 files  ± 0  1 272 suites  ±0   1h 13m 5s ⏱️ +36s
8 776 tests + 2  8 713 ✅ + 2  63 💤 ±0  0 ❌ ±0 
9 100 runs   - 55  9 030 ✅  - 56  70 💤 +1  0 ❌ ±0 

Results for commit b2bbc3d. ± Comparison against base commit 398d3ea.