Listen for dreaming state changes in BubblesManager

Fixes a bug with bubbles remaining hidden if keyguard dismissed event is
received before dreaming stops.

Bubbles are hidden when device is locked or is in dreaming state.
We have a callback to get notified of keyguard state changes.
That callback checks for both keyguard state and dreaming state.
We were not listening specifically for dreaming state changes.
This led to a bug with bubbles remaining hidden after device unlock.
We were not notified of dreaming state change and left the bubbles
hidden.
We were already listening for status bar events. This change includes a
check for dreaming state changes. If dreaming state changes and keyguard
is already dismissed, we show the bubbles.

Flag: NONE
Bug: 314124017
Test: atest SystemUITests:BubblesTest
Test: manual
    - have fingerprint lock set up on the device
    - open gmail
    - lock device
    - wait for screen to turn off, unlock device with fingerprint
    - trigger a bubble
    - observe that bubble is visible

Change-Id: Id58ad112828748fcc0709b1366fe447fc22f357b