Plasmashell : add dialog to manage containments when in edit mode

An UI to manage Screen assignment of Containments, the main use case is to recover lost or inactive panels from a display that you can no longer access.

qml part: plasma/plasma-desktop!618

related to https://phabricator.kde.org/T14346

CCBUG: 447044

Access the dialog from Toolbar in Edit Mode (Manage containments)
![Screenshot_20211222_114140](/uploads/31379781e3315a612d695220e623353b/Screenshot_20211222_114140.png)

![Screenshot_20211217_095945](/uploads/f890d5ac9f3ee6e82991d325b3078f5b/Screenshot_20211217_095945.png)


To show the dialog, simply enter in `edit mode`, then you can :
* See known displays and their panels and desktops, the dialog automatically update when adding/moving/removing a panel.
* Delete a panel or a desktop
* Recover a panel by moving it to an active display (click on move icon, then select the proper action in drop menu)
* Recover a desktop by moving it to an active display...