This moves the actual printing using QPrinter to the WebEngineWidgets
part of the API.
The printsupport module depends on the widgets module and therefore
QtWebEngineCore also had a dependency to widgets. This is removed by
this change.

Change-Id: If6e5745709a59de18f2123b930cbe6e64390c867
Reviewed-by: Michal Klocek <michal.klocek@qt.io>