[SB][Chips] Use distinctUntilChanged for statusBarHeadsUpState.

The status bar chips re-create their data model each time the heads up
state flow emits a value. But, they don't need to re-create their data
model if the heads up state hasn't changed, so add a
`#distinctUntilChanged` so that the flow doesn't emit if the state is
the same. This will prevent extra re-compositions of the status bar
chips.

Bug: 393456147
Flag: android.app.ui_rich_ongoing
Test: have 1 notification chip, then open & close shade -> verify 0
recompositions during shade open, and 1 recomposition during shade close
(instead of 1 during open and 2 during close)

Change-Id: I7e8394e289278a8780f1729c120dd80e90f1b520