Add dream component name to dream start/stop events logging.

In order to add the additional information, created dedicated
DreamUIEventLogger and moved the DREAM_START/STOP events in there.

Android Metrics Design Review: eldar/189451700.

Bug: 213906448
Test: Manually on device via `statsd_testdrive `
Change-Id: I37f4d70e5dd0bd2c516ef49b8f11c61530db6101