yuzu/main: Move window title updating logic to its own function

For similar reasons to the previous change, we move this to a single
function, so we don't need to duplicate the conversion logic in several
places within main.cpp.

src/yuzu/main.h

@@ -209,6 +209,7 @@ private slots:
 
 private:
     std::optional<u64> SelectRomFSDumpTarget(const FileSys::ContentProvider&, u64 program_id);
+    void UpdateWindowTitle(const QString& title_name = {});
     void UpdateStatusBar();
 
     Ui::MainWindow ui;