yuzu/main: Save settings when starting guest

Saves UISettings and Settings when booting a guest. Moves updating
UISettings::values from GMainWindow::closeEvent into its own function,
then reuses it in GMainWindow::BootGame.

src/yuzu/main.h

@@ -257,6 +257,7 @@ private:
                            const std::string& title_version = {});
     void UpdateStatusBar();
     void UpdateStatusButtons();
+    void UpdateUISettings();
     void HideMouseCursor();
     void ShowMouseCursor();
     void OpenURL(const QUrl& url);