Extract ChangeAttributeFactory from ChangeQueryProcessor

Introduce a new BeanProvider interface to pass to the create method.
This will allow the interface to be reused for other codepaths, namely
GetChange. Other than switching to the new class names, this should not
significantly impact plugin implementations.

Change-Id: Id318739f1e75e8f0f5981b2d2fd23993fba7e5c1

java/com/google/gerrit/server/change/PluginDefinedAttributesFactory.java

@@ -0,0 +1,23 @@
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.change;
+
+import com.google.gerrit.extensions.common.PluginDefinedInfo;
+import com.google.gerrit.server.query.change.ChangeData;
+import java.util.List;
+
+public interface PluginDefinedAttributesFactory {
+  List<PluginDefinedInfo> create(ChangeData cd);
+}