Add AppTransition type and remote animation for Dream in occluding Keyguard.

The existing Keyguard Occlude Animation Runner doesn't match the spec
for Dream in. It animates activity expanding from the center of the
screen. For Dream in, we have:
  - Dream fading in
  - DreamOverlay complications fading in slightly delayed, with each part
    starting at different times.

This CL adds dedicated AppTransitionType and remote animation runner,
which animates Dream fading in. It doesn't implement the separate
animation for DreamOverlay complications.

Bug: 222507937
Bug: 240477956
Bug: 242864189
Fix: 240477956
Test: on device, wait for Keyguard to time out to Dream.
Change-Id: I5517ded2eea77ea962ca1551ed51dd997ff09993