The PlasmaShell interface allows to create a PlasmaShellSurface for a
given Surface. Through this interface the Surface can request:
* a specific position
* a window type
So far only the window types Normal, Panel and Desktop are supported
which is a sufficient subset for getting plasmashell to work.
In future there should be security checks so that only the dedicated
desktop shell can bind these interfaces.
If there is a visible internal window it gets the pointer events.
The assumption is that the last created internal window is the top
most in stacking order.
We need a shared window id in some way to e.g. properly support TabBox.
Though I do not like that the return value is xcb_window_t. This should
be either changed or a new "generic" windowId needs to be introduced.
If the ShellClient got created for a Qt internal window, we try to
find the QWindow and if we get one, we use the geometry directly as
it got set by KWin in the first place.
Also a windowId() is added to ShellClient which can be used by the
effect system to find an EffectWindow. If it's an internal QWindow
we just use that window id. For other clients we still need some
smart solution.
The ShellClient is a Toplevel subclass for a
KWayland::Server::ShellSurfaceInterface. It gets created when a new
ShellSurfaceInterface is created and destoryed when it gets unmapped.
So far the usage is still rather limited. The ShellClient is opened
at position (0/0). While it's possible to pass pointer events to it,
it's not yet possible to activate it, so no keyboard focus.
