Restructure the public API for server

pkg/analysis_server/test/services/index/dart_index_contributor_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.services.src.index.dart_index_contributor;
 
-import 'package:analysis_server/analysis/index_core.dart';
+import 'package:analysis_server/plugin/index/index_core.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/index/index_contributor.dart';
 import 'package:analysis_server/src/services/index/index_store.dart';
 import 'package:analysis_server/src/services/index/indexable_element.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:typed_mock/typed_mock.dart';
@@ skipping 1705 matching lines @@
   RecordedRelation(this.indexable, this.relationship, this.location);
 
   @override
   String toString() {
     return 'RecordedRelation(indexable=$indexable; relationship=$relationship; '
         'location=$location; flags='
         '${location.isQualified ? "Q" : ""}'
         '${location.isResolved ? "R" : ""})';
   }
 }