Summary:
The idea behind the debugging console is to have a feature comparable
to xprop and xwininfo just for Wayland. We cannot have command line
utils as that violates the security restrictions, thus it needs to be
exposed directly in KWin.

The debugging console is invoked through DBus:
qdbus org.kde.KWin /KWin showDebugConsole

This opens a window with a tree view. The DebugConsoleModel which is
used by the tree view groups all windows into four categories:
* x11 clients (that is Workspace::clientList() and Workspace::desktopList())
* x11 unmanaged (Workspace::unmanagedList())
* wayland shell clients (WaylandServer::clients())
* wayland internal clients (KWin's own QWindows - WaylandServer::internalClients())

Each window is a child to one of the four categories. Each window itself
has all it's QProperties exposed as children.

This allows to properly inspect KWin's internal knowledge for windows and
should make it easier to investigate problems. E.g. what's a window's
...