Sometimes it's needed to show a native dialog for another process,
for example in xdg-desktop-portal-kde. In this case we have WId
of a parent window which can be used for calling
QWindow::setTransientParent(QWindow::fromWinId(...)).
Pass this transient parent to a native dialog so it could use
it as a transient parent for itself. Rename
QDialogPrivate::parentWindow() for clarity.
Change-Id: I68974ddea35f9366a0ddffe602d9d028f45e26fa
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
f05cc4144e