EGLFS: Don't raise the main window when docking

EGLFS doesn't honour that the floating windows should be
on top and will make the floating windows go behind.

It's also unneeded to raise it on eglfs, since it's fullscreen.

(cherry-picked from commit d06c6e8f11)

src/qtcommon/Window_qt.h

@@ -54,6 +54,8 @@ public:
     QPoint fromNativePixels(QPoint) const override;
     void startSystemMove() override;
 
+    bool isFullScreen() const override;
+
 protected:
     QPointer<QWindow> m_window;