add logging for Launcher backup and restore events

Test: Manually verify logs
Bug: 294386159
Change-Id: Ic3a77f4a09556e0d769837129e0bd094f1e91b6b

src/com/android/launcher3/model/LoaderTask.java

@@ -374,6 +374,8 @@ public class LoaderTask implements Runnable {
             final HashMap<PackageUserKey, SessionInfo> installingPkgs =
                     mSessionHelper.getActiveSessions();
             installingPkgs.forEach(mApp.getIconCache()::updateSessionCache);
+            FileLog.d(TAG, "loadWorkspace: Packages with active install sessions: "
+                    + installingPkgs.values());
 
             final PackageUserKey tempPackageKey = new PackageUserKey(null, null);
             mFirstScreenBroadcast = new FirstScreenBroadcast(installingPkgs);