[Enhancement] Drag parent onto child

[UnePierre]

Abstract

Steps to see the situation

1. Start Firefox with clean profile.
2. Install TST.
3. Open several tabs in a small tree
4. Try to drag&drop the parent (A) of a tree onto one of its offspring.

A (selected)
\- B
|\- B1 (drag here)
\- C

Expected result

B
\- B1
|\- A
\- C

5. The selected parent (A) should move and become a child of the offspring it was dragged onto (B1).
6. Another node becomes the parent; possibly the one that would get this position, when the parent was to be closed (B in the example).

This would also exchange the two nodes in a mini-tree (single-mom with only child) in a single action, which was my motivating example.

Actual (present) result

5. Nothing happens.

Environment

• Platform (OS): Windows10 x64
• Version of Firefox: 125.0.2 (32-Bit)
• Version (or revision) of Tree Style Tab: 3.9.19