Explicitly bind ChangeIndexCollection to allow use in plugins

Follow up patch to Id54b985692ca41ffcaabe9793d8b9035cb1d4e82 change.

Change-Id: I8c453ae490994ad1258c5b9b1045918911bf703c
Signed-off-by: Jacek Centkowski <geminica.programs@gmail.com>

gerrit-server/src/main/java/com/google/gerrit/server/index/IndexModule.java

@@ -84,6 +84,7 @@ public class IndexModule extends LifecycleModule {
   @Override
   protected void configure() {
     bind(IndexRewriter.class);
+    bind(ChangeIndexCollection.class);
     listener().to(ChangeIndexCollection.class);
     factory(ChangeIndexer.Factory.class);
   }