Fix QQuickWidget offscreen surface format and creation order

Create the QOffscreenSurface together with, and after, the QOpenGLContext.
This is essential to get a surface that is compatible with the context and
is in line with the QOffscreenSurface usage recommendation from the docs.

Otherwise, if the offscreen surface gets created first, without
knowing what _actual_ format (e.g. EGL configuration) the context
will use, the result is an incompatible surface and context on
systems that offer a different set of configurations for window and
pbuffer surfaces.

This fixes QQuickWidget on EGL implementations that offer both 16 and 24
bit pbuffer configs, but only 24 (or 32) bit window configs.

Task-number: QTBUG-39474
Change-Id: I43925d2b25e28d26d172ce9d22651c25b281b832
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Fix opacity issue in the renderer.

Given the following tree:

OpacityNode
    |
TransformNode (which is a batch root)
    |
GeometryNode

If both opacity and transform nodes were changed this frame, we would
hit the optimized "scrolling" path while traversing the tree and abort
updating that subtree. As a result the opacity change was not
propegated to the geometry node and it would be rendered incorrectly.

Fix this by skipping the optimized path when there are opacity changes
in an ancestor.

Task-number: QTBUG-39190
Change-Id: Ieaebfe3de62b961204bd3103fe9913d60e75e412
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>