Merge the dart:uri library into dart:core and update the Uri class

pkg/analyzer_experimental/lib/src/generated/sdk.dart

 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.sdk;
 
-import 'dart:uri';
 import 'java_core.dart';
 import 'java_engine.dart';
 import 'source.dart' show ContentCache, Source, UriKind;
 import 'engine.dart' show AnalysisContext;
 
 /**
  * Represents a single library in the SDK
  */
 abstract class SdkLibrary {
   /**
@@ skipping 231 matching lines @@
   List<String> get uris;
   /**
    * Return the source representing the library with the given {@code dart:} URI, or {@code null} if
    * the given URI does not denote a library in this SDK.
    * @param contentCache the content cache used to access the contents of the mapped source
    * @param dartUri the URI of the library to be returned
    * @return the source representing the specified library
    */
   Source mapDartUri(ContentCache contentCache, String dartUri);
 }