[Qt] Use WebPageProxy::postMessageToInjectedBundle when passing messages to a specific page in the builtin bundle
https://bugs.webkit.org/show_bug.cgi?id=105928

Reviewed by Simon Hausmann.

Simplify the code since we now can send the contents as is, instead of packaging it inside
an array that also contained the reference for the page. This was made possible after
r126311.

* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::setNavigatorQtObjectEnabled):
(QQuickWebViewExperimental::postMessage):
Built the messages and used WebPageProxy::postMessageToInjectedBundle() directly.

* UIProcess/qt/QtWebContext.cpp: Removed functions that now are simpler and were inlined in
qquickwebview.cpp.
* UIProcess/qt/QtWebContext.h: Ditto.
* WebProcess/qt/QtBuiltinBundle.cpp:
(WebKit::QtBuiltinBundle::initialize): Used the callback that gets messages for specific
pages. Also changed the way we create the bundle client: now we fill the struct with zeros,
and then set the fields we care about. This way if another field is added to that client,
this code doesn't need to be changed.
(WebKit::QtBuiltinBundle::didReceiveMessageToPage):
(WebKit::QtBuiltinBundle::handleMessageToNavigatorQtObject): Changed to not read the page
reference from the message, since we get it in the callback already.
(WebKit::QtBuiltinBundle::handleSetNavigatorQtObjectEnabled): Ditto.
* WebProcess/qt/QtBuiltinBundle.h:
(QtBuiltinBundle):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138723 268f45cc-cd09-0410-ab3c-d52691b4dbfc