[Qt][WK2] Make loading errors API easier to use.

[Qt][WK2] Make loading errors API easier to use.
https://bugs.webkit.org/show_bug.cgi?id=68357

Reviewed by Tor Arne Vestbø.

Make the API to get loading errors easier to use. 95197 introduced
a QJSValue API that is a bit opaque for the client code. Rather than
using a dedicated object, we can just pass the needed information as
parameters of the slot.

* UIProcess/API/qt/qdesktopwebview.cpp:
(QDesktopWebViewPrivate::loadDidFail):
* UIProcess/API/qt/qdesktopwebview.h:
* UIProcess/API/qt/qdesktopwebview_p.h:
* UIProcess/API/qt/qtouchwebpage.h:
* UIProcess/API/qt/tests/commonviewtests/tst_commonviewtests.cpp:
(tst_CommonViewTests::loadNonexistentFileUrl):
* UIProcess/API/qt/tests/commonviewtests/webviewabstraction.cpp:
(WebViewAbstraction::WebViewAbstraction):
(WebViewAbstraction::touchViewLoadFailed):
(WebViewAbstraction::desktopViewLoadFailed):
* UIProcess/API/qt/tests/commonviewtests/webviewabstraction.h:
* UIProcess/qt/QtWebPageProxy.cpp:
(QtWebPageProxy::loadDidFail):
* UIProcess/qt/TouchViewInterface.cpp:
(WebKit::TouchViewInterface::loadDidFail):
* UIProcess/qt/TouchViewInterface.h:
* UIProcess/qt/ViewInterface.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@95472 268f45cc-cd09-0410-ab3c-d52691b4dbfc