Re-enable _writeObjectId for element-text dumps, and update tests to reflect this change.

Change-Id: I5deecf685111bc3f2a5c18a69221e1e22978d10e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/438320
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: fshcheglov

pkg/analyzer/test/src/summary/element_text.dart

@@ -667,8 +667,7 @@ class _Element2Writer extends _AbstractElementWriter {
     // }
 
     _sink.writeIndentedLine(() {
-      // TODO(scheglov): restore after merging element model rewrite
-      // _writeObjectId(e);
+      _writeObjectId(e);
       if (e.isRequiredPositional) {
         _sink.write('requiredPositional ');
       } else if (e.isOptionalPositional) {