LibGUI+WindowServer: Add new WMEvent Super+Space

To make Assistant useful we need a way to quickly trigger it. I've
added a new specialized event coming from the window server for when a
user is holding down 'Super' and hits 'Space'.

The Taskbar will be able to listen for this event and spawn a new
instance of the Assistant if it's not already running.

Userland/Libraries/LibGUI/Event.h

@@ -63,6 +63,7 @@ public:
         WM_WindowIconBitmapChanged,
         WM_AppletAreaSizeChanged,
         WM_SuperKeyPressed,
+        WM_SuperSpaceKeyPressed,
         __End_WM_Events,
     };
 
@@ -102,6 +103,14 @@ public:
     }
 };
 
+class WMSuperSpaceKeyPressedEvent : public WMEvent {
+public:
+    explicit WMSuperSpaceKeyPressedEvent(int client_id)
+        : WMEvent(Event::Type::WM_SuperSpaceKeyPressed, client_id, 0)
+    {
+    }
+};
+
 class WMAppletAreaSizeChangedEvent : public WMEvent {
 public:
     explicit WMAppletAreaSizeChangedEvent(const Gfx::IntSize& size)