[Test Week] Add unit tests for UserCache

6 new methods tested.
added 1 method to help with testing.
no previous test class.

Bug: 353303621
Test: unit test
Flag: TEST_ONLY
Change-Id: I27e607df91bacc1a5dc5adc3b76a2f1758404e6a

src/com/android/launcher3/pm/UserCache.java

@@ -183,6 +183,11 @@ public class UserCache implements SafeCloseable {
         mUserToSerialMap.put(userHandle, info);
     }
 
+    @VisibleForTesting
+    public void putToPreInstallCache(UserHandle userHandle, List<String> preInstalledApps) {
+        mUserToPreInstallAppMap.put(userHandle, preInstalledApps);
+    }
+
     /**
      * @see UserManager#getUserProfiles()
      */