WindowServer: Add a custom window type for Launcher

This keeps it out of the taskbar window list.
The stacking order is a little gnarly, but it seems to work OK still.

Servers/WindowServer/WSWindow.cpp

@@ -140,6 +140,8 @@ static WSAPI_WindowType to_api(WSWindowType ws_type)
         return WSAPI_WindowType::Tooltip;
     case WSWindowType::Menubar:
         return WSAPI_WindowType::Menubar;
+    case WSWindowType::Launcher:
+        return WSAPI_WindowType::Launcher;
     default:
         ASSERT_NOT_REACHED();
     }