Restructure the public API for server

pkg/analysis_server/lib/plugin/index/index.dart

Index: pkg/analysis_server/lib/plugin/index/index.dart
diff --git a/pkg/analysis_server/lib/plugin/index.dart b/pkg/analysis_server/lib/plugin/index/index.dart
similarity index 94%
rename from pkg/analysis_server/lib/plugin/index.dart
rename to pkg/analysis_server/lib/plugin/index/index.dart
index 1e5b05c49f435a1689cdff4c496b43a1f5f65e62..b87fce9adc36ea095fb85368a61e4b16bdfb7c25 100644
--- a/pkg/analysis_server/lib/plugin/index.dart
+++ b/pkg/analysis_server/lib/plugin/index/index.dart
@@ -28,9 +28,9 @@
  *       ...
  *     }
  */
-library analysis_server.plugin.index;
+library analysis_server.plugin.index.index;
 
-import 'package:analysis_server/analysis/index_core.dart';
+import 'package:analysis_server/plugin/index/index_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:plugin/plugin.dart';