[Qt][WK2] Export QNetworkReply in the QtWebKit QML module.

[Qt][WK2] Export QNetworkReply in the QtWebKit QML module.
https://bugs.webkit.org/show_bug.cgi?id=68401

Reviewed by Simon Hausmann.

Add QNetworkReply in the QtWebKit module. We use the enum QNetworkReply::NetworkError
as the error code when the load fails. It is not used in the QtQuick module therefore
the QML team thinks it should belong here. Also added some auto-tests to cover the
loading errors.

* UIProcess/API/qt/qmlplugin/plugin.cpp:
(WebKit2QmlPlugin::registerTypes):
* UIProcess/API/qt/tests/qmltests/DesktopWebView/tst_loadFail.qml: Added.
* UIProcess/API/qt/tests/qmltests/TouchWebView/tst_loadFail.qml: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@95545 268f45cc-cd09-0410-ab3c-d52691b4dbfc