Nested TabControl adorner visual bug

[bors97]

Describe the bug
In case of a nested TabControl when dragging a TabItem the adorner's top part sinks to the child TabControl's height. Another (possibly) related bug is that you can drag on the child TabItem and it starts dragging the parent TabItem that is straight above the dragged child TabItem.

To Reproduce
Steps to reproduce the behavior:

1. Create a nested tabcontrol
2. Enable Drag and Drop on the parent Tab
3. Drag either the parent or child TabItem.

Expected behavior
The adorner's top part is on the top of the dragged item.

Screenshots

Desktop (please complete the following information):

• OS: Windows 11

[bors97]

After some testing the issue seems to be that the GetVisualDescendents method searches by depth for the TabPanel instead of breadth, which leads to it finding the content's TabControl's TabPanel first. Replacing the current search with a breadth-first search algorithm seems to solve the issue.