layer-shell-qt feature freeze exception

[Vlad Zahorodnii]

Hello,

I'd like to backport 
https://invent.kde.org/plasma/layer-shell-qt/-/merge_requests/89 to 6.6. 
This extends the API so it is possible to specify the explicit screen 
where a layer surface should be shown.

This can be used to fix bugs where certain plasma windows are placed 
incorrectly.

Currently, layer-shell-qt monitors QWindow::screen() but it can 
unexpectedly change after calling QWindow::create() or functions that 
change the window geometry. The new APIs should make plasma window 
placement more robust.

The changes are API compatible for Plasma/6.6.

Regards,
Vlad