Allow forcing active focus on focus scope controls

I'd like to remove MouseArea from the basic VKB example:

https://codereview.qt-project.org/#/c/218682/3/

There are two problems preventing this:

1. When interactive, Flickable steals press events (see QTBUG-66132 for a solution to this)
2. Giving a Pane that is a parent of the Flickable ClickFocus does not result in child text fields losing active focus when clicking outside of them, as there is a sub-focus child (?).