[Qt][WK2] Move startDrag implementation to QtWebPageEventHandler

[Qt][WK2] Move startDrag implementation to QtWebPageEventHandler
https://bugs.webkit.org/show_bug.cgi?id=73145

Reviewed by Simon Hausmann.

Move QtWebPageProxy::startDrag to QtWebPageEventHandler::startDrag
and call it straight from QtPageClient.

* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::QQuickWebViewPrivate):
* UIProcess/qt/QtWebPageEventHandler.cpp:
(dragOperationToDropAction):
(dragOperationToDropActions):
(dropActionToDragOperation):
Now these functions are static inline and not part of QtWebPageEventHandler
anymore.

(QtWebPageEventHandler::QtWebPageEventHandler):
(QtWebPageEventHandler::startDrag):
* UIProcess/qt/QtWebPageEventHandler.h:
* UIProcess/qt/QtWebPageProxy.cpp:
(QtWebPageProxy::startDrag): removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@102579 268f45cc-cd09-0410-ab3c-d52691b4dbfc