Includes foreground services in top notification section.

This change modifies the various components which treat high-priority
notifications differently, including the status bar, the lockscreen, and
the notification layout algorithm, such that foreground service
notifications are always included among the high-priority notifications.
This logic is now centralized in NotificationData.

Bug: 116622974
Bug: 118805186
Test: manually
Change-Id: Ia13c1aac0cf91c400594df96ce267e768133f8d1