Revert part of the RenderWidgetHostViewQtDelegate refactoring

This reverts parts of commit 9c198939be1ef064d1a2430a4b9991f2fe16f359.

This does keeps the popup fixes and removes support for
QWebEnginePage::setViewportSize and QWebEnginePage::render until
we can evaluate the needs vs the cost of such feature.

Change-Id: I1b55b751d463717b1462393ea8cd353422f8fdbb
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Render the widgets view using the scene graph into a QOpenGLWidget

This means that widgets application now need to setup the GL context
sharing as well. QWebEngineWidgets::initialize() must be called,
which has the same effect as QWebEngine::initialize().
The QtWebEngineWidgets now depends on the QtWebEngine module to make
this happen.

Since QOpenGLWidget is only available in Qt 5.3, this patch also
disables the webenginewidgets module completely when building using
Qt 5.2.

Change-Id: I0e99a779d1eb080f2ccf5a338ff0763ad64e6eba
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Get rid of the BackingStore rendering path

Now that the widgets view is also using the delegated renderer,
there are no supported configuration that use the BackingStore
rendering path, itself on the way of deprecation in Chromium.

Change-Id: I4ab889f6a7c65e8447c259faf2c7a98b88c1acf5
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Remove the RenderWidgetHostViewQtDelegateQuickBase template

We now only have a QQuickItem subclass and this isn't needed anymore.

Change-Id: I3a10943e54f52d1554dc76ccc1841aaacd5171e2
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>