fix: position of desktop glass pane with mirroring

- on Wayland, a widget can only positioned to a specific screen
  if it is full-screen
- when control screen was to the right of the display screen,
  the position changed when mirroring was enabled
- always show the glass pane as full-screen to fix this

Signed-off-by: letsfindaway <me@letsfindaway.de>

Author: letsfindaway

src/desktop/UBDesktopAnnotationController.cpp

@@ -360,13 +360,7 @@ void UBDesktopAnnotationController::showWindow()
 
     UBDrawingController::drawingController()->setStylusTool(mDesktopStylusTool);
 
-#ifndef Q_OS_LINUX
     UBPlatformUtils::showFullScreen(mTransparentDrawingView);
-#else
-    // this is necessary to avoid hiding the panels on Unity and Cinnamon
-    // if finer control is necessary, use qgetenv("XDG_CURRENT_DESKTOP")
-    mTransparentDrawingView->show();
-#endif
     UBPlatformUtils::hideMenuBarAndDock();
 
     mDesktopPalette->appear();