support OnScreenDisplay window type

plasmashell needs some of their windows as on screen display
ideally only the shell will be allowed to use them
REVIEW:125036

src/wayland/plasmashell_interface.cpp

@@ -227,6 +227,9 @@ void PlasmaShellSurfaceInterface::Private::setRole(uint32_t role)
     case ORG_KDE_PLASMA_SURFACE_ROLE_PANEL:
         r = Role::Panel;
         break;
+    case ORG_KDE_PLASMA_SURFACE_ROLE_ONSCREENDISPLAY:
+        r = Role::OnScreenDisplay;
+        break;
     case ORG_KDE_PLASMA_SURFACE_ROLE_NORMAL:
     default:
         r = Role::Normal;

src/wayland/plasmashell_interface.h

@@ -69,7 +69,8 @@ public:
     enum class Role {
         Normal,
         Desktop,
-        Panel
+        Panel,
+        OnScreenDisplay
     };
     Role role() const;
     enum class PanelBehavior {