Added private event flag for committed states

DisplayInfo currently sends display changed callbacks when display state
or the display committed state changes. Given a state change is followed
by a committed state change, users would often get 2 callbacks for a
single state change. To address this, the committed state is now being
ported to a separate private event for clients specifically interested
in this. Given committed state is a hidden field, we can be confident
that there are no apps interested in callbacks when this field changes

Bug: 342192387
Flag: com.android.server.display.feature.flags.committed_state_separate_event
Test: atest DisplayEventTest
Change-Id: I53b311f0bbc408acfd4cf02c8b1581506c957ab6