shell/panelview: restart unhide timer on drag leave
Reason for the change
Otherwise the autohide and dodge windows panels don't rehide when leaving them during drag and drop.
On the kwin side, kwin!6191 (merged) is needed.
Test plan
(Based on kwin!6191 (merged))
- Create a dodge-windows/auto hide panel and make it hide.
- Drag a folder onto the edge with the panel
- observe that the panel unhides
- drag away from the panel
- observe that the panel rehides
- again, drag onto the panel and drop
- move mouse away
- observe that the panel rehides.