Inflate taskbar all apps in abstract slide-in view.

All apps can now be dismissed via the scrim or swiping down. To properly
behave as an AFW, the apps view can no longer be within the taskbar's
layout, and will instead add and remove itself from the drag layer.

Test: Manual
Bug: 204696617
Change-Id: I86a0ffc06faa653c65b3797a57ba6512c6874221