Ability to disable / replace built-in handles and touch selection menu

With 5.13 Peter added https://codereview.qt-project.org/c/qt/qtwebengine/+/233633 touch handles and a touch selection menu. While Chromium doesn't give the ability to disable / replace these, it would be great if we still had the ability in Qt.

We implemented our own handles and menu, which has customized buttons etc., now of course with that change we have 2x the menu and the handles.

Another step could be to extend the API to be able to override the handles / touch menu with a custom one directly.