Promote frequently sharing apps as per monthly stats fetched from...

Promote frequently sharing apps as per monthly stats fetched from UsageStatsManager, in case PeopleService does not store enough sharing events when users just swicth to Sharesheet ranking in PeopleService.
   
Bug: 156320324
Test: atest com.android.server.people.prediction.ShareTargetPredictorTest
Test: atest com.android.server.people.prediction.SharesheetModelScorerTest
Test: atest com.android.server.people.data.UsageStatsQueryHelperTest

Change-Id: Iae7a3a8195ae4901cd1d9d673fe0cf8a27845488