Fix rendering bug with batched translucent elements.

When one item in a batch of other translucent items would
change opacity, we need to rebuild batches under the current
root as all items in a batch are expected to have the same
opacity.

Task-number: QTBUG-34311
Change-Id: I2b9db19f05bd3a82be65cfa8a91e9398e8d58d0f
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Added private API for enabling sharing between the QQuickwindow instances.

This API is primarily a hook which is needed by the Qt WebEngine to
set up sharing with the scene graph's OpenGL contexts.

Change-Id: I5bb03abd9ab99f502db8e413fe838a8b30365b8d
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
KeyNavigation should use forceActiveFocus

It would only set focus which works fine as long as the target is in the
same FocusScope. But as user one would expect that the target actually
receives the focus. Using forceActiveFocus is sensible since the current
item needs to have the "activeFocus" anyway and within the same focus
scope setting focus=true on another item will take away the active
focus.

Task-number: QTBUG-34209

Change-Id: I824f15fd0d4d42eb2f0c6c1b02660f2e007b3362
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Fix build using clang

Change-Id: I59ceac7b3b68a92f128b0ee78076182d191e09e9
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>