Fix0r up PolicyClient...
[Qt][WK2] Remove direct references to WebPageProxy from QQuickWebPage.
[WK2] Add C API to copy selected files from WebOpenPanelParameters.
[Qt][WK2] Use C API to enable Navigator Qt Object.
[Qt][WK2] Extend QRawWebView classes for use as base API.
[Qt][WK2] Move QQuickWebView on top of QRawWebView.
Let QtWebPageEventHandler use QRawWebView.

And let it not know any WebKit2 internals.
This makes it necessary to do some conversion in QtPageClient, which will eventually be done
in QRawWebViewPrivate when it starts acting as a PageClient (the implementation for that is
already there.)
Let QQuickWebPage and QtWebPageSGNode use QRawWebView.
Move PageClient and PageViewportController to QRawWebView.
Add proper API includes and move platform initialization to QRawWebView.
Remove references to CoordinatedGraphicsScene.
Remove some more dependencies.