desktop-shell: support disallow-output-changed-move

With this, when unplugging an extended display, the view displayed on
the extended display won't be re-positioned to other displays.

On some embedded devices, the views are often fullscreen displayed, even
on the extended displays. When disconnecting the extended displays, the
views are not desired to be moved onto the existing displays. Without
this change, we can see the view flash across the existing displays
even though the UI program hides the view as soon as it can, which is
unexpected.

Signed-off-by: Paul Pu <hui.pu@gehealthcare.com>