Expose QWizardPrivate::updateLayout() as a public method of QWizard

In case when the layout of the already shown wizard page changes (e.g. after pressing some button on the page we show additional widget), there is no way of forcing the layout system to properly recalculate the layout. As a consequence, the wizard e.g. doesn't expand when a new widget is shown and the part of the widget may be cropped.

So, basically there is a need to call sometimes QWizardPrivate::updateLayout() on demand, as it's done internally by QWizard itself when transitioning between pages.

As a reference please see https://codereview.qt-project.org/c/qt-creator/qt-creator/+/322560. Currently we use a hacky solution there: we are calling m_wizard->setTitleFormat(m_wizard->titleFormat()) as we rely on that the implementation of setTitleFormat sets the format and calls QWizardPrivate::updateLayout() unconditionally.