Introduce DreamLog using LogBuffer.

This change introduces a DreamLogger which uses a LogBuffer. It also
logs the overlay animations state to this buffer.

Bug: 274804854
Test: adb shell dumpsys activity service
com.android.systemui/.SystemUIService DreamLog -> verify overlay
animation states are dumpped

Change-Id: Ie1a811cdc52a3584796f04872c2f2e605587051f