Overhaul Auto-Type Action Handling

* Close #2603 - Add support for modifier syntax (+, ^, and %)
* Fix #2633 - Allow reference syntax {REF:...} in Auto-Type sequences
* Close #5334  - Tell the user which part of the Auto-Type sequence is invalid for easy correction
* Fix #2401 - Select the right window on macOS prior to starting Auto-Type

* Allow for nested placeholders

src/gui/MainWindow.h

@@ -87,6 +87,7 @@ public slots:
     void bringToFront();
     void closeAllDatabases();
     void lockAllDatabases();
+    void closeModalWindow();
     void displayDesktopNotification(const QString& msg, QString title = "", int msTimeoutHint = 10000);
     void restartApp(const QString& message);