[WIP] MPV: Use Qt calls to make the widget go fullscreen

src/UI/DocumentViews/MpvContainer.cc

@@ -314,10 +314,12 @@ void
 MpvContainer::toggleFullScreenState() noexcept
 {
     if (isFullScreen()) {
-        printMpvError(mpv_set_property_string(mpv, "fullscreen", "no"));
+        setWindowState(Qt::WindowMaximized);
+        showFullScreen();
         qDebug() << "Toggle fullscreen: set to normal";
     } else {
-        printMpvError(mpv_set_property_string(mpv, "fullscreen", "yes"));
+        setWindowState(Qt::WindowFullScreen);
+        showNormal();
         qDebug() << "Toggle fullscreen: set to fullscreen";
     }
 }