Host: Add GetTopLevelWindowInfo()

And use it for screensaver inhibiting on Linux.

src/duckstation-qt/qtutils.h

@@ -1,4 +1,5 @@
 #pragma once
+#include "common/window_info.h"
 #include "common/types.h"
 #include <QtCore/QByteArray>
 #include <QtCore/QMetaType>
@@ -91,4 +92,10 @@ QIcon GetIconForRegion(DiscRegion region);
 QIcon GetIconForEntryType(GameList::EntryType type);
 QIcon GetIconForCompatibility(GameDatabase::CompatibilityRating rating);
 
+/// Returns the pixel ratio/scaling factor for a widget.
+qreal GetDevicePixelRatioForWidget(const QWidget* widget);
+
+/// Returns the common window info structure for a Qt widget.
+std::optional<WindowInfo> GetWindowInfoForWidget(QWidget* widget);
+
 } // namespace QtUtils