Move general index classes from gerrit-server to gerrit-index

These classes do not depend on any Gerrit server functionality, and
could even be used to define an index without depending on the
gerrit-server package. This allows for a clearer separation of BUILD
rules; the QueryParser and antlr targets don't escape the gerrit-index
package.

The general layout thus far is to put index definition code in
com.google.gerrit.index, and query-related code (predicates, etc.)  in
com.google.gerrit.index.query.

The gerrit-index package is still of limited utility on its own, because
QueryProcessor and InternalQuery still live in the server package, and
untangling their dependencies will still be a bit more work.

Change-Id: I3c4616d08ecf19d5ccd1b9b91b3fd0b1fcedd901

gerrit-index/src/main/java/com/google/gerrit/index/IndexRewriter.java

@@ -0,0 +1,23 @@
+// Copyright (C) 2016 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.index;
+
+import com.google.gerrit.index.query.Predicate;
+import com.google.gerrit.index.query.QueryParseException;
+
+public interface IndexRewriter<T> {
+
+  Predicate<T> rewrite(Predicate<T> in, QueryOptions opts) throws QueryParseException;
+}