Introduce IsHighPriorityProvider

The IsHighPriorityProvider caches the isHighPriority
value for ListEntries instead of requiring the
NotificationRankingManager to set the value.

To interface with the current notification pipeline, we
use the GroupManager to look for grouping information, but
this code will eventually be deleted (b/145659174)

Test: atest GroupEntryTest NotificationEntryTest IsHighPriorityProviderTest NotificationRankingManagerTest
Test: atest SystemUiTests
Bug: 145134683
Change-Id: I24fbfddb648183552eb46d6b94cbb726e64468c8