Reparent children when hiding preserved surface.

A recent change hides preserved surfaces immediately
when showing the new surface. We need to make sure to
reparent the children at this point like we do when we
destroy.

Bug: 79748420
Test: go/wm-smoke. Manual.
Change-Id: Ia5b68d595c4cdc1395ffcc69de7128c04f9e248d