[SB][Notif] Re-tapping notif chip hides the HUN.

Tapping on a notification status bar chip shows the notification as a
HUN. Re-tapping on the chip should hide the HUN.

Fixes: 385728177
Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips

Test: atest HeadsUpCoordinatorTest

Test: Have status bar notif chip, tap it -> verify HUN shows up. Tap
chip again while HUN is showing -> verify HUN disappears.
Test: Have status bar notif chip, tap it -> verify HUN shows up. Let it
time out. Tap status bar notif chip again -> verify HUN appears again.
Test: Have two 2 chips, tap one chip, then the other chip -> verify
other chip's HUN appears

Change-Id: Id593f946bf7a4e4cdf1899a536af412261639b20