Restructure the public API for server

pkg/analysis_server/lib/src/domains/analysis/navigation_dart.dart

 // Copyright (c) 2015, 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 domains.analysis.navigation_dart;
 
-import 'package:analysis_server/analysis/navigation_core.dart';
+import 'package:analysis_server/plugin/analysis/navigation/navigation_core.dart';
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
 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/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 /**
  * A computer for navigation regions in a Dart [CompilationUnit].
  */
@@ skipping 309 matching lines @@
     }
     // The node starts or ends in the range.
     if (isInRange(node.offset) || isInRange(node.end)) {
       node.accept(visitor);
       return;
     }
     // Go deeper.
     super.visitNode(node);
   }
 }