[Qt] Enable QML handling of crashed/unresponsive QtWebProcess

https://bugs.webkit.org/show_bug.cgi?id=108474

Forward the processDidCrash, didRelaunchProcess, processDidBecomeUnresponsive
and processDidBecomeResponsive signals to QML's WebView.experimental.

Reviewed by Jocelyn Turcotte.

* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::processDidCrash):
(QQuickWebViewPrivate::didRelaunchProcess):
(QQuickWebViewPrivate::processDidBecomeUnresponsive):
(QQuickWebViewPrivate::processDidBecomeResponsive):
* UIProcess/API/qt/qquickwebview_p.h:
* UIProcess/API/qt/qquickwebview_p_p.h:
(QQuickWebViewPrivate):

NOTE: This is the initial iteration of the patch attached to upstream
bug report 108474, i.e.:
https://bug-108474-attachments.webkit.org/attachment.cgi?id=185771
The actually committed version is incompatible with the status of
QtWebKit stable as the architecture changed too much.

Change-Id: I91d28dde2774fd1487a96ac36a14b522ffb7756c
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153580 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>