[SB][Chips] Add UI events for chip show and chip hide.

Log when chips are added or removed from the list so that we can get a
sense of how often people have multiple chips.

Bug: 386821418
Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips
Test: Use atom tester to verify the events log at the right times

Change-Id: If71fae0a85d557bc8b070b03928aabc420050246