Materialize IdentifiedUser deps in BatchUpdate

When executing BatchUpdates from a receive commit, materialise the user
dependent objects so that it can be passed over to other threads
for delayed execution outside the current scope.

P.S. This fixes Gerrit master breakages caused by OutOfScopeException.

Change-Id: Ic463ddaeb5d9c90573a3a4639523f214125aaaad

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -825,8 +825,9 @@ public class ReceiveCommits {
       return;
     }
 
-    try (BatchUpdate bu = batchUpdateFactory.create(db,
-          magicBranch.dest.getParentKey(), user, TimeUtil.nowTs());
+    try (BatchUpdate bu =
+        batchUpdateFactory.create(db, magicBranch.dest.getParentKey(),
+            user.materializedCopy(), TimeUtil.nowTs());
         ObjectInserter ins = repo.newObjectInserter()) {
       bu.setRepository(repo, rp.getRevWalk(), ins)
           .updateChangesInParallel();