Dismiss HUN group summary if user taps HUN group child

If an app posts a group with a summary and 2+ children and sets
GROUP_ALERT_SUMMARY, System UI will present the summary with the
collapsed children as a single HUN.

If the user expands one of the children and taps it, the animation code
will try to remove the HUN for the child the user tapped. Unfortunately,
since the *summary* was the alerting notification, the entire group HUN
will remain visible.

This can also happen if an app posts a group with a high-priority
summary but default (or lower) priority children.

This change augments the logic in removeHun so that if the notification
itself isn't alerting, but it has a parent that *is* alerting, the
*parent's* HUN will be removed instead.

Bug: 249840069
Test: manual, using Notify.apk
Test: atest 'NotificationLaunchAnimatorControllerTest#testHunIsRemovedAndCallbackIsInvokedOnAlertingParent'
Test: atest TapChildOfHeadsUpSummary
Change-Id: Ia5b8537747def402df518d33f14ed7c8e2198585