QOpenGLWidget: Can't set/read V-Sync

QOpenGLWidget setFormat() "ignores" swap interval. In QOpenGLWidgetPrivate::initialize() method swap interval is set to TLW, but the TLW is not re-created, so it doesn't make any effect.

Comment inside initialize() method: "Most platforms will pick up the changed swap interval on the next makeCurrent or swapBuffers." - it doesn't work as expected. The window needs destroy() and create() to "read" the new format. I think that swap interval should have an exception (it shouldn't need to re-create) to make this comment real, because recreating the TLW can cause ficker.

The second thing is that QOpenGLWidget::format() doesn't return the format proper with swap interval value.