Host: Add GetTopLevelWindowInfo()

And use it for screensaver inhibiting on Linux.

src/duckstation-qt/mainwindow.cpp

@@ -2520,6 +2520,13 @@ void MainWindow::checkForSettingChanges()
   updateWindowState();
 }
 
+void MainWindow::getWindowInfo(WindowInfo* wi)
+{
+  std::optional<WindowInfo> opt_wi(QtUtils::GetWindowInfoForWidget(this));
+  if (opt_wi.has_value())
+    *wi = opt_wi.value();
+}
+
 void MainWindow::onCheckForUpdatesActionTriggered()
 {
   // Wipe out the last version, that way it displays the update if we've previously skipped it.