Add parser support for using a URI in a part-of directive

pkg/analyzer/lib/src/dart/ast/utilities.dart

Index: pkg/analyzer/lib/src/dart/ast/utilities.dart
diff --git a/pkg/analyzer/lib/src/dart/ast/utilities.dart b/pkg/analyzer/lib/src/dart/ast/utilities.dart
index 8e45f3c37f9e160eb4c9e9848d129052ee55bfcf..7dd0e48010e4b202c1072313332910fcccab9273 100644
--- a/pkg/analyzer/lib/src/dart/ast/utilities.dart
+++ b/pkg/analyzer/lib/src/dart/ast/utilities.dart
@@ -740,6 +740,7 @@ class AstCloner implements AstVisitor<AstNode> {
           cloneNodeList(node.metadata),
           cloneToken(node.partKeyword),
           cloneToken(node.ofKeyword),
+          cloneNode(node.uri),
           cloneNode(node.libraryName),
           cloneToken(node.semicolon));
 
@@ -3480,6 +3481,7 @@ class IncrementalAstCloner implements AstVisitor<AstNode> {
         _cloneNodeList(node.metadata),
         _mapToken(node.partKeyword),
         _mapToken(node.ofKeyword),
+        _cloneNode(node.uri),
         _cloneNode(node.libraryName),
         _mapToken(node.semicolon));
     copy.element = node.element;