[Qt] Use the existing inheritedOpacity/matrix properties of QSGNode

[Qt] Use the existing inheritedOpacity/matrix properties of QSGNode
https://bugs.webkit.org/show_bug.cgi?id=79543

Use QSGNode::inheritedOpacity() and QSGNode::matrix().
Also, remove flags from changedStates() that we don't actually touch.
This is covered by existing API tests.

Reviewed by Kenneth Rohde Christiansen.

* UIProcess/API/qt/qquickwebpage.cpp:
(QQuickWebPagePrivate::paintToCurrentGLContext):
(PageProxyNode::changedStates):
(PageProxyNode::render):
* UIProcess/API/qt/qquickwebpage_p_p.h:
(QQuickWebPagePrivate):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@109664 268f45cc-cd09-0410-ab3c-d52691b4dbfc