qml runtime tool have no option to share opengl context

Previously Qt was bundled with `qmlscene` tool considered to be used for testing.

Later the `qml` tool was introduced intended for production usage scenarios.

However in contrast to `qmlscene` the newer tool have no option to set `AA_ShareOpenGLContext` option resulting into poor performance.

The attached example plays video from YouTube using QtWebEngine component.

With `qmlscene` on given platform it produces ~25fps whereas with `qml` resulting fps is about ~12-13.

Same poor results could be achieved with `qmlscene` if using `--disable-context-sharing` or `–software` options.