Increase PerformBackupTask unit coverage 2

With KV Refactor in mind.
* Split empty queue test into multiple tests.
* Tests around packages failing backup pre-conditions.
* Added verifications for event logging.
* Renamed some tests to better reflect important parts of it.
* More tests about one package.
* Introduced PackageData to help mock packages, much like TransportData.
* Some small refactors.

Test: atest PerformBackupTaskTest
Change-Id: I23aba2b26e82f8643cc1c90f9408510ab34045fd
diff --git a/services/tests/servicestests/src/com/android/server/backup/DataChangedJournalTest.java b/services/tests/servicestests/src/com/android/server/backup/DataChangedJournalTest.java
index c27fd07..3cdeba6 100644
--- a/services/tests/servicestests/src/com/android/server/backup/DataChangedJournalTest.java
+++ b/services/tests/servicestests/src/com/android/server/backup/DataChangedJournalTest.java
@@ -36,6 +36,7 @@
 import java.io.File;
 import java.io.FileInputStream;
 import java.util.ArrayList;
+import java.util.function.Consumer;
 
 @SmallTest
 @Presubmit
@@ -47,7 +48,7 @@
 
     @Rule public TemporaryFolder mTemporaryFolder = new TemporaryFolder();
 
-    @Mock private DataChangedJournal.Consumer mConsumer;
+    @Mock private Consumer<String> mConsumer;
 
     private File mFile;
     private DataChangedJournal mJournal;