Document new link capturing methods in QtWebEngine

Where an HTML document is used as part of the user interface, and not to display external data, for example, when displaying a list of results, it is essential that link clicks can be delegated to the Qt app instead of being processed by the HTML handler engine.

This is possible with the venerable QTextBrowser, and also with Qt WebKit (QWebPage::setLinkDelegationPolicy()).

As far as I know, no such function exists in Qt WebEngine, which means that applications which use the page as part of the UI, cannot be migrated from WebKit to WebEngine. Actually, with only a little exageration, it seems that the latter does not allow much more than what could be done by calling system("chromium-browser")