Fix a bug with jittering dream overlay.

The first jitter causes all the dream overlay views to jump noticeably.
The issues was that the first jitter happens after the views have
appeared on screen. The solution is to jitter immediately so that the
views are already in their initial jitter position before they become
visible.

Test: atest DreamOverlayContainerViewControllerTest
Bug: 220182090
Change-Id: Ia62a5cf8d314a8617eaa522b51be99f61aef8b99