Disable some more qtbase examples for dynamic gl builds

Examples using OpenGL 1.x cannot be migrated. Therefore, similarly to ES
builds, we just disable them.

Change-Id: I76e888d2ecfb2582ae35853d9dcdd0cb686fddc6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Do not add QOffscreenSurface windows to the global list

QOffscreenSurface has to stay usable even after returning from app.exec().
Hence close()ing the underlying hidden window, that is used on platforms that
do not provide real offscreen surfaces, is wrong.

Normally all QWindows are closed (and thus destroy()'ed) when quitting the application,
meaning the the offscreen surface cannot be made current anymore after returning
from exec(). This is an unnecessary limitation and makes certain cleanup operations
impossible.

Task-number: QTBUG-39908
Change-Id: Iea1489378a18f29ff84ba8f13a6dad2d66d2b315
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Include QMetaType in the native context headers

Just to be safe. The Q_DECLARE_METATYPE needs this.
And including some Qt header is necessary anyways.

Change-Id: I6e97493434760f37a79e735293cef8d4213c2e11
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Cleanup local var usage

Change-Id: I24c8bc1eef444e3ef4823d5d092089e4f308585b
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Enablers for QQuickWidget render() support.

Add a QImage based fallback for renderToTexture widgets, and use
that when rendering to something else than a QWidgetBackingStore.

Change-Id: I415a3a27c4ecb4ddbac45181c5a568b01ac5cb7a
Task-number: QTBUG-39562
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>