Introduce dream suppression

This change adds the outlet for suppressing dreams. And currently there
is only one reason for suppressing dreams, which is that the device is
currently in a vehicle.

Test: atest DreamSuppressionStartableTest
Bug: 433984504
Flag: com.android.systemui.dream_suppression
Change-Id: Iac8952112e080c6a97670bcb81c3c9520fcb91da