Rename two more classes to prepare for the public API

pkg/analysis_server/test/services/index/store/codec_test.dart

Index: pkg/analysis_server/test/services/index/store/codec_test.dart
diff --git a/pkg/analysis_server/test/services/index/store/codec_test.dart b/pkg/analysis_server/test/services/index/store/codec_test.dart
index 1ea46fc65f64e8dc859545edd5ec4e7eaf79a66c..7c134ed4137f5412a6377a779b5ec41d9ccbb81f 100644
--- a/pkg/analysis_server/test/services/index/store/codec_test.dart
+++ b/pkg/analysis_server/test/services/index/store/codec_test.dart
@@ -389,7 +389,8 @@ class _RelationshipCodecTest {
   }
 
   void test_all() {
-    Relationship relationship = Relationship.getRelationship('my-relationship');
+    RelationshipImpl relationship =
+        RelationshipImpl.getRelationship('my-relationship');
     int id = codec.encode(relationship);
     expect(codec.decode(id), relationship);
   }