[Qt][WK2] Replace use of WebPreferences with use of WKPrefences C API
https://bugs.webkit.org/show_bug.cgi?id=108952

Reviewed by Simon Hausmann.

Signed off for WebKit2 by Benjamin Poulain.

This patch moves the view classes and preferences in the Qt API
to use the C API for accessing and manipulating preferences as
part of the cleanup and move towards using the C API as base for
the Qt WebKit2 API.

Adds the function WebKit::adoptToQString for convenience when
dealing with QString and copied String objects.

Removes the ScrollAnimatorEnabled options from QWebPreferences.

* UIProcess/API/cpp/qt/WKStringQt.cpp:
(WebKit::adoptToQString):
* UIProcess/API/cpp/qt/WKStringQt.h:
(WebKit):
* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::initialize):
* UIProcess/API/qt/qwebpreferences.cpp:
(QWebPreferencesPrivate::testAttribute):
(QWebPreferencesPrivate::setAttribute):
(QWebPreferencesPrivate::setFontFamily):
(QWebPreferencesPrivate::fontFamily):
(QWebPreferencesPrivate::setFontSize):
(QWebPreferencesPrivate::fontSize):
* UIProcess/API/qt/qwebpreferences_p.h:
* UIProcess/API/qt/qwebpreferences_p_p.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144165 268f45cc-cd09-0410-ab3c-d52691b4dbfc